Method and device for transmitting/receiving synchronization signal in wireless cellular communication system

ABSTRACT

The present disclosure relates to a communication method and system for converging a 5th-Generation (5G) communication system for supporting higher data rates beyond a 4th-Generation (4G) system with a technology for Internet of Things (IoT). The present disclosure may be applied to intelligent services based on the 5G communication technology and the IoT-related technology, such as smart home, smart building, smart city, smart car, connected car, health care, digital education, smart retail, security and safety services. The present invention is a method by which a base station transmits a signal in a wireless communication system for efficiently performing an initial access procedure of a terminal, the method comprising the steps of: generating the synchronization signal on a basis of subcarrier spacing used in the synchronization signal; and transmitting the synchronization signal to the terminal.

TECHNICAL FIELD

One embodiment of the present disclosure relates to a wirelesscommunication system, and more particularly, to a method and a systemfor efficient transmission and reception by a terminal in case where aplurality of subcarrier spacings are supported in one system in order toefficiently provide various services required in a next-generationmobile communication system. Further, another embodiment of the presentdisclosure relates to a wireless communication system, and moreparticularly, to a method and a device in which different wirelesscommunication systems coexist on one carrier frequency or plural carrierfrequencies, and a terminal capable of transmitting/receiving data in atleast one of the different communication systems transmits and receivesthe data with the respective communication systems.

BACKGROUND ART

To meet the demand for wireless data traffic having increased sincedeployment of 4G communication systems, efforts have been made todevelop an improved 5G or pre-5G communication system. Therefore, the 5Gor pre-5G communication system is also called a ‘Beyond 4G Network’ or a‘Post LTE System’. The 5G communication system is considered to beimplemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, soas to accomplish higher data rates. To decrease propagation loss of theradio waves and increase the transmission distance, the beamforming,massive multiple-input multiple-output (MIMO), Full Dimensional MIMO(FD-MIMO), array antenna, an analog beam forming, large scale antennatechniques are discussed in 5G communication systems. In addition, in 5Gcommunication systems, development for system network improvement isunder way based on advanced small cells, cloud Radio Access Networks(RANs), ultra-dense networks, device-to-device (D2D) communication,wireless backhaul, moving network, cooperative communication,Coordinated Multi-Points (CoMP), reception-end interference cancellationand the like. In the 5G system, Hybrid FSK and QAM Modulation (FQAM) andsliding window superposition coding (SWSC) as an advanced codingmodulation (ACM), and filter bank multi carrier (FBMC), non-orthogonalmultiple access(NOMA), and sparse code multiple access (SCMA) as anadvanced access technology have been developed.

The Internet, which is a human centered connectivity network wherehumans generate and consume information, is now evolving to the Internetof Things (IoT) where distributed entities, such as things, exchange andprocess information without human intervention. The Internet ofEverything (IoE), which is a combination of the IoT technology and theBig Data processing technology through connection with a cloud server,has emerged. As technology elements, such as “sensing technology”,“wired/wireless communication and network infrastructure”, “serviceinterface technology”, and “Security technology” have been demanded forIoT implementation, a sensor network, a Machine-to-Machine (M2M)communication, Machine Type Communication (MTC), and so forth have beenrecently researched. Such an IoT environment may provide intelligentInternet technology services that create a new value to human life bycollecting and analyzing data generated among connected things. IoT maybe applied to a variety of fields including smart home, smart building,smart city, smart car or connected cars, smart grid, health care, smartappliances and advanced medical services through convergence andcombination between existing Information Technology (IT) and variousindustrial applications.

In line with this, various attempts have been made to apply 5Gcommunication systems to IoT networks. For example, technologies such asa sensor network, Machine Type Communication (MTC), andMachine-to-Machine (M2M) communication may be implemented bybeamforming, MIMO, and array antennas. Application of a cloud RadioAccess Network (RAN) as the above-described Big Data processingtechnology may also be considered to be as an example of convergencebetween the 5G technology and the IoT technology.

Recently, with the development of 5G communication system, researchesfor satisfying various requirements and services in the 5G communicationsystem have been made.

DISCLOSURE OF INVENTION Technical Problem

In 5th generation wireless cellular communication system (hereinafter,5G communication system), it is required to provide various serviceshaving different transmission/reception techniques andtransmission/reception parameters in one system in order to satisfyvarious user requirements and services, and it is important to designthe system so that any service to be added is not restricted by thecurrent system in consideration of forward compatibility. As an exampleof a method for supporting various services in a 5G communicationsystem, according to the present disclosure, a system for supporting aplurality of subcarrier spacings in one system may be considered. Insuch a 5G communication system, a terminal is unable to know thesubcarrier spacing used in the system during an initial access process,and this may cause a problem that the initial access cannot beefficiently performed. Accordingly, in the present disclosure, it isnecessary to provide a device and a method in which a terminal intendingto access the 5G communication system can efficiently detect thesubcarrier spacing supported by the system and then perform the initialaccess process.

Further, another aspect of the present disclosure is to provide a methodand a device in which, as a scheme for satisfying the maximum delay timein time division duplex (TDD), subframes are divided into a plurality oftypes in the TDD, and data transmission/reception is provided not toexceed the maximum delay time in consideration of a specific subframetype among the respective divided subframe types as a subframe that canbe dynamically changed as uplink and downlink subframe. Further, stillanother aspect of the present disclosure is to provide a method and adevice for resource allocation for 5G beyond future services using thedynamic uplink/downlink change subframes and subframes in FDD.

Solution to Problem

In accordance with an aspect of the present disclosure to solve theabove-described problems, a method by a base station for transmitting asignal in a wireless communication system includes generating asynchronization signal based on a subcarrier spacing used for thesynchronization signal; and transmitting the synchronization signal to aterminal. The subcarrier spacing may be detected based on a repeatpattern of a time domain appearing when the synchronization signal isdetected by the terminal.

In accordance with another aspect of the present disclosure, a method bya terminal for receiving a signal in a wireless communication systemincludes receiving a synchronization signal generated based on asubcarrier spacing used for the synchronization signal; and determiningthe subcarrier spacing based on the synchronization signal.

In accordance with still another aspect of the present disclosure, abase station transmitting a signal in a wireless communication systemincludes a transceiver configured to transmit and receive signals with aterminal; and a controller configured to generate a synchronizationsignal based on a subcarrier spacing used for the synchronizationsignal, and control the transceiver to transmit the synchronizationsignal to the terminal.

In accordance with yet still another aspect of the present disclosure, aterminal receiving a signal in a wireless communication system includesa transceiver configured to transmit and receive signals with a basestation; and a controller configured to control the transceiver toreceive a synchronization signal generated based on a subcarrier spacingused for the synchronization signal, and determine the subcarrierspacing based on the synchronization signal.

Advantageous Effects of Invention

According to the aspects of the present disclosure as described above,in order to satisfy various user requirements and services, a structureand a method are provided, in which a terminal can efficiently detect asubcarrier spacing and can perform an initial access in a 5Gcommunication system supporting a plurality of subcarrier spacings.

Further, according to the aspects of the present disclosure, as a schemefor satisfying the maximum delay time in TDD for 5G, a method and adevice are provided, in which subframes are divided into a plurality oftypes in the TDD, and data transmission/reception is provided not toexceed the maximum delay time in consideration of a specific subframetype among the respective divided subframe types as a subframe that canbe dynamically changed as uplink and downlink subframe. Further, amethod and a device for resource allocation are provided for 5G beyondfuture services using the dynamic uplink/downlink change subframes andsubframes in FDD. On the other hand, other various effects will bedisclosed directly or suggestively in the detailed description accordingto the aspects of the present disclosure to be described later.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating subcarrier spacing of an OFDM systemused for modulation and demodulation of uplink and downlink signals in a5G communication system considered in the present disclosure;

FIG. 2 is a diagram illustrating an example for supporting a singlesubcarrier spacing within one system as an example of a 5G communicationsystem considered in the present disclosure;

FIG. 3 is a diagram illustrating an example of a method in which aterminal discovers a subcarrier spacing in a process of performing aninitial access of a 5G communication system through the terminal;

FIG. 4 is a diagram illustrating an example for supporting a pluralityof subcarrier spacings within one system as an example of a 5Gcommunication system considered in the present disclosure;

FIG. 5 is a diagram illustrating an embodiment in which asynchronization signal is transmitted in a 5G communication systemconsidered in the present disclosure;

FIG. 6 is a diagram illustrating a method for constantly mappingsequences of a synchronization signal at equal frequency spacingsregardless of subcarrier spacings used for the synchronization signalaccording to an embodiment of the present disclosure;

FIG. 7 is a diagram illustrating a method in which a terminal receiverdetects subcarrier spacings of a synchronization signal in case ofdifferently mapping synchronization sequences in accordance with thesubcarrier spacings used for the synchronization signal according to anembodiment of the present disclosure;

FIG. 8 is a flowchart illustrating a method in which a terminal detectssubcarrier spacings by performing an initial access using asynchronization structure proposed in the present disclosure accordingto an embodiment of the present disclosure;

FIG. 9 is a block diagram illustrating the configuration of atransmission unit of a base station for performing the above-describedembodiments of the present disclosure;

FIG. 10A is a block diagram illustrating the internal structure of aterminal reception unit according to an embodiment of the presentdisclosure;

FIG. 10B is a block diagram illustrating the configuration of a basestation according to an embodiment of the present disclosure;

FIG. 11 is a diagram illustrating the basic structure of atime-frequency domain in an LTE system;

FIG. 12 is a diagram illustrating an example in which 5G services aremultiplexed and transmitted in one system;

FIG. 13A is a diagram illustrating an example of a communication systemto which the present disclosure is applied;

FIG. 13B is a diagram illustrating another example of a communicationsystem to which the present disclosure is applied;

FIG. 14 is a diagram illustrating an example in which 5G for eachsubframe type is operated in TDD;

FIG. 15 is a diagram illustrating another example in which 5G for eachsubframe type is operated in TDD;

FIGS. 16A and 16B are diagrams illustrating procedures of a base stationand a terminal according to an embodiment of the present disclosureoperating 5G for each subframe type in TDD;

FIG. 17 is a diagram illustrating an example for providing forwardcompatibility for each subframe type in TDD;

FIG. 18 is a diagram illustrating another example for providing forwardcompatibility for each subframe type in FDD;

FIGS. 19A and 19B are diagrams illustrating procedures of a base stationand a terminal according to an embodiment of the present disclosure forproviding forward compatibility for each subframe type;

FIG. 20 is a diagram illustrating the configuration of a base stationdevice according to the present disclosure; and

FIG. 21 is a diagram illustrating the configuration of a terminal deviceaccording to the present disclosure.

MODE FOR THE INVENTION

Hereinafter, embodiments of the present disclosure will be described indetail with reference to the accompanying drawings. In describing thepresent disclosure, related well-known functions or configurationsincorporated herein are not described in detail in case where it isdetermined that they obscure the subject matter of the presentdisclosure in unnecessary detail. Further, terms to be described laterare terms defined in consideration of their functions in the presentdisclosure, but may differ depending on intentions of a user and anoperator or customs. Accordingly, they should be defined on the basis ofthe contents of the whole description of the present disclosure.

The aspects and features of the present disclosure and methods forachieving the aspects and features will be apparent by referring to theembodiments to be described in detail with reference to the accompanyingdrawings. However, the present disclosure is not limited to theembodiments disclosed hereinafter, but can be implemented in diverseforms. The matters defined in the description, such as the detailedconstruction and elements, are nothing but specific details provided toassist those of ordinary skill in the art in a comprehensiveunderstanding of the disclosure, and the present disclosure is onlydefined within the scope of the appended claims. In the entiredescription of the present disclosure, the same drawing referencenumerals are used for the same elements across various figures.

First Embodiment

A wireless communication system was initially developed for the purposeof providing a voice-oriented service, but has been developed as abroadband wireless communication system that provides a high-speed andhigh-quality packet data service like communication standards, such as3GPP high speed packet access (HSPA), long term evolution (LTE) orevolved universal terrestrial radio access (E-UTRA), LTE-advanced(LTE-A), LTE-A Pro, 3GPP2 high rate packet data (HRPD), ultra-mobilebroadband (UMB), and IEEE 802.16e.

In the LTE system that is a representative example of the broadbandwireless communication systems, downlink (DL) adopts an orthogonalfrequency division multiplexing (OFDM) scheme, and uplink (UL) adoptssingle carrier frequency division multiple access (SC-FDMA) scheme. Theuplink means a radio link in which a terminal (or user equipment (UE))or a mobile station (MS) transmits data or a control signal to a basestation (BS) (or eNode B (eNB)), and the downlink means a radio link inwhich the base station transmits data or a control signal to theterminal. According to the above-described multiple access schemes, dataof respective users or control information can be discriminated fromeach other by performing an allocation and an operation so as to preventtime-frequency resources for carrying the data or control informationfor each user from overlapping each other, that is, to establishorthogonality.

As the post LTE communication system, the 5G communication system shouldsupport services that simultaneously satisfy various requirements ofusers and service providers since it is required to freely reflect thevarious requirements. Services being considered for the 5G communicationsystem include enhanced mobile broadband (hereinafter, eMBB), massivemachine type communication (hereinafter, mMTC), and ultra-reliabilitylow-latency communication (hereinafter, URLLC).

The eMBB aims to provide a more improved data rate than the data ratesupported by the existing LTE, LTE-A, or LTE-A Pro. For example, in the5G communication system, the eMBB should provide, from the viewpoint ofone base station, the maximum transmission rate of 20 Gbps in thedownlink, and the maximum transmission rate of 10 Gbps in the uplink.Further, the 5G communication system should provide the maximumtransmission rate and a user perceived data rate of an increasedterminal. In order to satisfy such requirements, it is required toimprove various transmission/reception technologies including moreimproved multi-input multi-output (MIMO) transmission technology.Further, the current LTE system transmits signals using the maximum 20MHz transmission bandwidth in the 2 GHz band, whereas the 5Gcommunication system uses a wider frequency bandwidth than 20 MHz in thefrequency band of 3 to 6 GHz or 6 GHz or more, and thus can satisfy thedata rate required in the 5G communication system.

At the same time, the mMTC is under consideration to support applicationservices, such as the Internet of things (IoT), in the 5G communicationsystem. In order to efficiently provide the Internet of things, the mMTCshould satisfy requirements, such as massive terminal connection supportin a cell, terminal coverage improvement, improved battery time, andterminal cost reduction. Since the Internet of things is attached toseveral sensors and various devices to provide communication functions,it should support a large number of terminals (e.g., 1,000,000terminals/km²) in the cell. Further, since there is a high possibilitythat the terminal supporting the mMTC is located in a shaded area thatthe cell is unable to cover, such as underground of a building, due tothe service characteristics, a wider coverage is required as comparedwith other services provided in the 5G communication system. Theterminal supporting the mMTC should be inexpensive, and requires verylong battery life time, such as 10 to 15 years, since it is difficult tofrequently replace a battery of the terminal.

Last, the URLLC is a cellular-based wireless communication service usedfor a specific purpose (mission-critical). For example, services may beused for remote control of a robot or machinery, industrial automation,unmanned aerial vehicle, remote health care, and emergency alert.Accordingly, the communication provided by the URLLC should provide verylow latency and very high reliability. For example, a service supportingthe URLLC should satisfy air interface latency that is shorter than 0.5ms, and requires a packet error rate of 10⁻⁵ or less at the same time.Accordingly, for the service supporting the URLLC, the 5G system shouldprovide a transmit time interval (TTI) that is smaller than those ofother services, and also requires a design to allocate wide resources inthe frequency band in order to secure reliability of a communicationlink.

As described above, for the services that should be provided in the 5Gcommunication system, different transmission/reception techniques andtransmission/reception parameters may be used to satisfy differentrequirements of the respective services. As an example, it may beconsidered that the respective services have different subcarrierspacings in accordance with the requirements. Here, the subcarrierspacing means a spacing in which a plurality of subcarriers constitutingthe communication system based on orthogonal frequency divisionmultiplexing (OFDM) or orthogonal frequency division multiple access(OFDMA) are put in the frequency domain.

FIG. 1 is a diagram illustrating subcarrier spacing of an OFDM systemused for modulation and demodulation of uplink and downlink signals in a5G communication system considered in the present disclosure.

Referring to FIG. 1, an OFDM system may be explained through divisioninto a frequency domain 100 and a time domain 110. The OFDM systemperforms quadrature phase shift keying (QPSK) or quadrature amplitudemodulation (QAM) of data to be transmitted, and then maps correspondingsymbols to respective subcarriers 120 in the frequency domain 100. Inthe frequency domain 100, the OFDM system is composed of a plurality ofsubcarriers 120, and the plurality of subcarriers 120 are located to bespaced apart from each other for a subcarrier spacing (Δf) 130. Asdescribed above, in order to efficiently support various services andvarious carrier frequencies in the 5G communication system, it isconsidered that a plurality of subcarrier spacings 130 are supported inone system bandwidth.

At present, in order to support a plurality of subcarriers in the 5Gcommunication system, two schemes have been considered. As the firstmethod for supporting a plurality of subcarriers in the 5G communicationsystem, a subcarrier spacing set that the 5G communication system canhave may be determined using mathematical expression 1 below.

Δf=f ₀ M  [Mathematical Expression 1]

Here, f₀ denotes a basic subcarrier spacing of the system, and M denotesa scaling factor. For example, if f₀ is 15 kHz, the subcarrier spacingset that the 5G communication system can have may be composed of 7.5KHz, 15 KHz, 30 KHz, 45 KHz, 60 KHz, and 75 KHz, and the system can beconfigured using the whole or a part of the corresponding set.

Further, as the second method for supporting a plurality of subcarriersin the 5G communication system, a subcarrier spacing set that the 5Gcommunication system can have may be determined using mathematicalexpression 2 below.

Δf=f ₀2^(m)  [Mathematical Expression 2]

Here, f₀ denotes a basic subcarrier spacing of the system, and m denotesan integer scaling factor. For example, if f₀ is 15 kHz, the subcarrierspacing set that the 5G communication system can have may be composed of7.5 KHz, 15 KHz, 30 KHz, 60 KHz, and 120 KHz. In this case, the systemcan also be configured using the whole or a part of the correspondingset. In describing the present disclosure, it is assumed that thesubcarrier spacing set of 15 KHz, 30 KHz, 60 KHz, and 120 KHz is used ina state where f₀ is 15 kHz in the 5G communication system in accordancewith the two methods as described above. However, even with respect toanother subcarrier spacing set (e.g., in case where f₀ is 17.5 kHz, andthe subcarrier spacing set is composed of 17.5 KHz, 35 KHz, 70 KHz, and140 KHz), the technology proposed in the present disclosure can beapplied without limit, and this will be described later through anembodiment of the present disclosure. In case of considering thesubcarrier spacing set composed of 17.5 KHz, 35 KHz, 70 KHz, and 140 KHzin the present disclosure, this may be mapped to the technology asdescribed above based on the case where f₀ is 15 kHz. Similarly, 35 kHz,70 kHz, and 140 kHz may be respectively mapped to 30 kHz, 60 kHz, and120 kHz in a one-to-one manner in describing the present disclosure.

Various subcarrier spacing sets as described above may be used forvarious purposes in one system. As an example, in a band having a lowcarrier frequency, such as 2 to 4 GHz band, it may be suitable to use alow subcarrier spacing in consideration of the channel situation of thecorresponding band (i.e., multi-path delay spread or coherencebandwidth). For example, since the path delay spread is relatively highand thus the coherence bandwidth is low in the carrier frequency of the2 to 4 GHz band, it is profitable to use a low subcarrier spacing. Atthe same time, since higher influence caused by the channel situationand Doppler shift and frequency offset is exerted in a band having acarrier frequency that is higher than 6 GHz, it may be preferable to usea high subcarrier spacing. Further, for the system having requirementsof very low transmission delay time, such as URLLC, even in case of aband using low carrier frequency, high subcarrier spacing may be used inthe 5G communication system.

In FIG. 1, the OFDM system in the time domain 110 is configured in theunit of an OFDM symbol 140 that is the minimum unit of the OFDM timedomain. The OFDM symbol 140 is configured by adding a cyclic prefix(hereinafter, CP) 160 to an IFFT symbol 150 that is obtained byperforming inverse fast Fourier transform (IFFT) of a plurality ofsubcarriers inserted into the frequency domain 100. The CP 160 may beconfigured by copying a signal located in the last portion of the IFFTsymbol to the front of the IFFT symbol 150. The IFFT symbol period 170is in reverse proportion to the subcarrier spacing (Δf) 130. That is, ifthe subcarrier spacing 130 is widened, the IFFT symbol length 170 isrelatively shortened, whereas if the subcarrier spacing 130 is narrowed,the IFFT symbol length 170 is lengthened in reverse proportion to thesubcarrier spacing 130. For such a reason, in a system requiring verylow transmission delay time, such as URLLC, a wide subcarrier spacingmay be preferred to make the IFFT symbol length short. The CP length 180is designed to minimize a power loss caused by the CP in a manner thatit is normally set to be larger than the multi-path delay spread, but tobe smaller than the IFFT symbol length 170.

As described above, in the 5G communication system, a plurality ofsubcarrier spacings can be supported in various methods in one system.FIG. 2 is a diagram illustrating an example of a 5G communication systemconsidered in the present disclosure for supporting a single subcarrierspacing within one system.

Referring to FIG. 2, a signal transmitted by a base station or aterminal in the 5G communication system may be composed of a pluralityof subframes 200. One subframe may be transmitted in one transmit timeinterval, and is composed of a plurality of OFDM symbols 220. Here, itis illustrated that one subframe 200 is composed of N OFDM symbols 220.Although it is assumed that one system uses only one subframe spacing inFIG. 2, a different subcarrier spacing may be used for each cell inaccordance with cell operating scenarios. For example, in the 5Gcommunication system using a low carrier frequency band (e.g., 2 to 4GHz), a signal can be generated and transmitted using a low subcarrierspacing, such as 15 KHz. In contrast, in the 5G communication systemusing a high carrier frequency band (e.g., 28 or 60 GHz), it ispreferable to use a high subcarrier spacing, such as 60 KHz inconsideration of frequency error offset and phase noise. However, incase of considering flexibility, it is not preferable that the use of aspecific subcarrier spacing is limited to a specific frequency band, andthus it is not excluded to use a high subcarrier band with respect to alow frequency band.

In case of using a different subcarrier spacing for each cell or systemalthough a single subcarrier is used in one 5G communication system asdescribed above, it is required for the terminal to know in advance thesubcarrier spacing used by the base station in order to receive adownlink signal. However, if a different subcarrier spacing of asynchronization signal, which is received by the terminal in an initialaccess process after power-on, is used for each cell or system, there isa problem that the base station cannot configure the subcarrier spacingto the terminal through explicit signaling, and thus the terminal itselfshould detect the subcarrier spacing.

Here, definition of the synchronization signal means a reference signalthat the base station transmits for time and frequency synchronizationand cell search when the terminal performs the initial access to thebase station, and in LTE, signals, such as a primary synchronizationsignal (PSS) and a secondary synchronization signal (SSS), may betransmitted for synchronization. In the present disclosure, signalsserving as the PSS and SSS may be considered for the time and frequencysynchronization and the cell search in the initial access process, or anadditional signal structure may be considered, regardless of the numberor kind of the signals used for the synchronization signals.

FIG. 3 is a diagram illustrating a first embodiment of a method in whicha terminal discovers a subcarrier spacing in a process of performing aninitial access in a 5G communication system if the terminal does notknow the subcarrier spacing of a cell intended to be accessed.

Referring to FIG. 3, if the terminal does not know the subcarrierspacing used in the 5G communication system as described above, it mayperform an initial access process with respect to all subcarrierspacings supported by the base station. That is, the terminal mayperform the initial access after changing terminal hardwareconfiguration (e.g., configuration of a radio frequency (RF) device,configuration of an analog-to-digital converter (ADC), and configurationof a baseband processor) with respect to one subcarrier spacing, and ifthe initial access has failed, the terminal may change the hardwareconfiguration to a next usable subcarrier spacing, and may again performthe initial access. If the initial access is completed with a specificsubcarrier spacing during performing the above-described process, theterminal may consider the corresponding subcarrier spacing as asubcarrier spacing used in the corresponding cell, and may use thereference timing and frequency offset detected using the correspondingsubcarrier spacing, and the cell search value for the forward terminaloperation.

In FIG. 3, operation 300 is an operation into which the terminal firstlyenters for the initial access after the power-on, and includes anoperation of selecting the lowest subcarrier spacing among thesubcarrier spacing set supported by the base station. In this case, itis assumed that the terminal is aware of all subcarrier spacingssupported by the base station. At operation 310, the terminal configuresa parameter corresponding to the corresponding subcarrier to hardware.As described above, in accordance with the subcarrier spacing, the OFDMsymbol length may differ, and the ADC sampling frequency may alsodiffer. Accordingly, the terminal should properly change theconfigurations of the RF device, the ADC, and the baseband processor soas to perform the synchronization in accordance with the correspondingsubcarrier spacing. At operation 320, the terminal performs time andfrequency synchronization and cell search while receiving the signal inaccordance with the hardware configuration at operation 310. The timeand frequency synchronization and the cell search may be performedthrough detection of the synchronization signal transmitted by the basestation. At operation 340, if the synchronization and the cell search iscompleted (i.e., if the synchronization signal is detected) within apreset specific time, the terminal considers that the base station hasused the subcarrier spacing assumed for the synchronization and the cellsearch, and completes the operation on the assumption that the detectionof the subcarrier spacing has been completed. In contrast, if thesynchronization and the cell search is not completed within the presetspecific time at operation 340, the terminal moves to operation 330 toselect a subcarrier spacing having a next size among subcarrier spacingsthat can be supported by the base station, and then moves to operation310 to continue the same process.

According to the embodiment explained through FIG. 3, the method by theterminal for detecting the subcarrier spacing requires to change thehardware configuration in the initial access process. Further, since anunnecessary process of detecting the synchronization signal with respectto various subcarrier spacings is required, terminal complexity isincreased, and a lot of time is necessary to perform the initial accessprocess. Accordingly, a method or a device by the base station fortransmitting a signal, which may cause an efficient terminal operation,is necessary in consideration of the terminal implementation complexityand time required for the initial access.

FIG. 4 is a diagram illustrating an example of a 5G communication systemconsidered in the present disclosure for supporting a plurality ofsubcarrier spacings within one system.

Referring to FIG. 4, a signal transmitted by a base station or aterminal in the 5G communication system may be composed of a pluralityof subframes 400, 410, and 420. In the system exemplified in FIG. 4,only one subcarrier spacing can be used in one subframe, but in anothersubframe, a signal in accordance with another subcarrier spacing can betransmitted. That is, signals having different subcarrier spacings maybe multiplexed and transmitted in time domain. As an example, subframe400 may use 15 kHz subcarrier spacing, and subframe 410 may use asubframe spacing corresponding to 30 kHz. If it is assumed that subframe400 and subframe 410 use the same number of OFDM symbols 430 and 440,subframe 400 may have a transmit time interval corresponding to TTI#1450, and subframe 410 may have a transmit time interval corresponding toTTI#2 460. Here, since the subcarrier spacing of subframe 400 is ½ ofthe subcarrier spacing of subframe 410, TTI#1 450 of subframe 400 has alength that is twice the length of TTI#2 460 of subframe 410. Similarly,it is exemplified that subframe 420 has a subcarrier spacingcorresponding to 7.5 KHz, and thus may have TTI#3 470 that is relativelya long transmit time interval.

The 5G communication system according to FIG. 4 may be considered as ascheme for efficiently operating various services. For example, in orderto provide an eMBB service, a signal may be transmitted using 15 kHzsubcarrier spacing in consideration of the channel situation of a lowfrequency band. In contrast, for a service requiring very lowtransmission delay, such as URLLC, a high subcarrier spacing, such as 30kHz, may be suitable. Further, in case of a terminal moving at highspeed, a high subcarrier spacing may be necessary to reduce performancedeterioration in accordance with Doppler shift, and a low subcarrierspacing may be useful in an mMTC or broadcasting system. In order tomaintain the coverage while maintaining the number of terminalssupportable in mMTC, a low subcarrier spacing is suitable. In thebroadcasting service (MBMS), a relatively long CP length is required toobtain a single frequency network diversity, and in order to reduce anoverhead having an increased CP length, a low subcarrier spacing may besuitable.

Even in case of supporting another subcarrier spacing for variousservices as described above, in the same manner as the example describedusing FIG. 2 as described above, there is a problem that the terminalshould detect the subcarrier spacing used for the synchronization signalin an initial synchronization process. That is, since the terminal doesnot know not only the subcarrier spacing used by the base station totransmit various services but also the subcarrier spacing used for thesynchronization signal, there is a problem that the terminal itselfshould detect the subcarrier spacing used for the synchronization signalin the initial access process. Even in the 5G communication systemexemplified in FIG. 4, the subcarrier spacing can be detected throughthe method as illustrated in FIG. 3, but, as described above, it isinefficient to do so in consideration of the terminal complexity andtime required for the initial access.

Further, although only a case where different subframes have differentsubcarrier spacings is exemplified in FIG. 4, even a case wheredifferent subcarrier spacings are provided in one subframe may beconsidered in order to efficiently provide services having variousrequirements. Even in this case, there is a problem that the terminalshould detect the subcarrier spacing of the synchronization signal.

FIG. 5 is a diagram illustrating an embodiment in which asynchronization signal is transmitted in a 5G communication systemconsidered in the present disclosure.

Referring to FIG. 5, a synchronization signal 500 may be transmitted ina predetermined period 530 on time axis 510. Further, thesynchronization signal 500 may be transmitted within a predeterminedsynchronization signal transmission bandwidth 540 on frequency axis 520.The synchronization signal makes it possible to map a special sequenceto a subcarrier in the transmission bandwidth 540 in order to indicateinformation required for the initial access of the terminal including acell ID. In the synchronization signal, a combination of one or aplurality of sequences may be mapped to the information including thecell ID, and the terminal can detect the ID of the cell to which theterminal intends to access by detecting the sequence used for thesynchronization signal. The sequence used for the synchronization signalmay be a sequence having constant amplitude zero auto correlation(CAZAC) characteristics, such as Zadoff-Chu sequence or Golay sequence,or a pseudo random noise sequence, such as M-sequence or Gold sequence.In the present disclosure, it is assumed that the above-described PSS orSSS is used for the synchronization signal, but the present disclosureis not described to be limited to any specific signal.

The synchronization signal 500 may be configured using one OFDM symbolor a plurality of OFDM symbols. In case where the synchronization signalis configured using a plurality of OFDM symbols, sequences for aplurality of different synchronization signals may be mapped to therespective OFDM symbols. As an example, in a similar manner to LTE, thePSS may be generated using three Zadoff-Chu sequences, and the SSS maybe generated using the Gold sequence.

The synchronization signal 500 may be transmitted using differentsubcarrier spacings in accordance with the frequency band used in thesystem or an environment in a similar manner to other services. Forexample, in a low frequency band, such as 2 or 4 GHz band, 15 or 30 kHzsubcarrier spacing may be used for generation and transmission of thesynchronization signal, whereas in a high frequency band, such as 6 GHzband, 60 kHz subcarrier spacing may be used for the generation andtransmission of the synchronization signal. However, as described above,it is not limited to use a specific subcarrier spacing in a specificfrequency band, and, if needed, the base station may configure varioussubcarrier spacings for the synchronization signal.

As described above, the terminal does not know the subcarrier spacingthat the base station managing a specific cell uses to transmit thesynchronization signal when the terminal performs the initial accesswith respect to the corresponding cell, and thus difficulty may occur inperforming the synchronization and cell search. Further, even in case ofperforming not only the initial access but also an adjacent cell searchfor measuring a handover and an adjacent cell, the terminal does notknow the subcarrier spacing that the synchronization signal of theadjacent cell uses, and thus difficulty may occur. In order to solvethis, as described above, a method in which the terminal performs theinitial access with respect to all subcarrier spacings that can besupported by the base station may be considered. However, this increasestime required in the initial access process, and thus is not suitable inconsideration of the initial access and the adjacent cell search.

According to a second embodiment of the present disclosure to bedescribed later, a synchronization signal structure and a transmissionmethod thereof are proposed, which enable the terminal to efficientlydetect the subcarrier spacing of the synchronization signal in theinitial access process. Further, according to the present disclosure, amethod and a device for the terminal to receive the synchronizationsignal are proposed, which enable the terminal to efficiently detect thesubcarrier spacing of the synchronization signal in the initial accessprocess. In the present disclosure, a case where the subcarrier spacingsupported in the 5G communication system is mainly 15 kHz, 30 KHz, 60KHz, and 120 KHz in a state where the basic subcarrier spacing is 15 kHzwill be described, but even in case where the basic subcarrier spacinghas a different frequency (e.g., 17.5 kHz), the embodiment described inthe present disclosure may be applied.

As the second embodiment of the present disclosure, a method and astructure of a synchronization signal for the initial access andadjacent cell search in the 5G communication system are proposed.

In the system supporting a plurality of subcarrier spacings, differentsynchronization signals should be defined in accordance with theplurality of subcarrier spacings, and the base station can transmit thesynchronization signal through proper selection of the subcarrierspacing of the synchronization signal in accordance with an environmentsupported by each cell and service requirements. Accordingly, thesynchronization signal having a different subcarrier spacing can betransmitted for each base station, and it is required for the terminalto detect the subcarrier spacing corresponding to the synchronizationsignal in the initial access and adjacent cell search process.

The present disclosure proposes a method for mapping sequences of thesynchronization signal always in the same location regardless of thesubcarrier spacing for transmitting the synchronization signal for theinitial access and adjacent cell search in the 5G communication systemthat can support a plurality of subcarrier spacings. According to theembodiment, the actual sequences of the synchronization signal may bemapped at equal frequency spacings regardless of the subcarrier spacingsused by the base station to transmit the synchronization signal.

FIG. 6 is a diagram illustrating a method for constantly mappingsequences of a synchronization signal at equal frequency spacingsregardless of subcarrier spacings used for the synchronization signalaccording to an embodiment of the present disclosure.

Referring to FIG. 6, a system 600 having 15 kHz subcarrier spacing, asystem 610 having 30 KHz subcarrier spacing, and a system 620 having 60KHz subcarrier spacing are considered. Here, it is assumed that themaximum supportable subcarrier spacing is 60 KHz in the 5G communicationsystem supporting a plurality of subcarrier spacings. In this case,rules used to map the actual sequences of the synchronization signal atequal frequency spacings regardless of the subcarrier spacings used forthe synchronization signal are as follows.

-   -   In the synchronization signal having 15 kHz subcarrier spacing,        the sequence used for the synchronization signal may be mapped        to every fourth subcarrier among subcarriers allocated for the        synchronization signal, and a null (or “0”) may be inserted into        the remaining subcarriers. That is, it is possible to apply a        comb-type structure in which the sequences used for the        synchronization signal are mapped to every four subcarriers.    -   In the synchronization signal having 30 kHz subcarrier spacing,        the sequence used for the synchronization signal may be mapped        to every second subcarrier among subcarriers allocated for the        synchronization signal, and a null (or “0”) may be inserted into        the remaining subcarriers. That is, it is possible to apply a        comb-type structure in which the sequences used for the        synchronization signal are mapped to every two subcarriers.    -   In the synchronization signal having 60 kHz subcarrier spacing,        the sequences used for the synchronization signal are mapped to        all subcarriers allocated for the synchronization signal. That        is, a structure is applied, in which sequences used for the        synchronization signal are mapped to all subcarriers without        considering the comb type.

In case of a synchronization signal 600 having 15 kHz subcarrier spacingin an embodiment according to FIG. 6, the sequence d(k) 630 used for thesynchronization signal is inserted into every fourth subcarrier, and anull is inserted into the remaining subcarriers 640. Similarly, in caseof a synchronization signal 610 having 30 kHz subcarrier spacing, thesequence d(k) 630 used for the synchronization signal is inserted intoevery second subcarrier, and a null is inserted into the remainingsubcarriers 640. In case of a synchronization signal 620 having 60 kHzsubcarrier spacing, the sequence d(k) 630 used for the synchronizationsignal is mapped to all subcarriers without null insertion.

That is, the sequence d(k) 630 used for the synchronization signal isinserted into a subcarrier corresponding to integer times the ratio ofthe maximum subcarrier spacing considered for the synchronization signalto the subcarrier spacing used for the current synchronization signal,and a null is inserted into the remaining subcarriers 640. As describedabove, if the sequence used for the synchronization signal is mappedusing the ratio of the maximum subcarrier spacing used for thesynchronization signal to the subcarrier spacing of the synchronizationsignal to be currently transmitted, the synchronization sequence can bemapped to the subcarrier at constant frequency spacings 650 regardlessof the subcarrier spacings. That is, the sequence used for thesynchronization signal may be mapped at constant frequency spacingsregardless of the subcarrier spacings used by the base station for thesynchronization signal. The base station may select the subcarrierspacing intended to be used for transmission of the synchronizationsignal, and may transmit the synchronization signal in accordance withthe embodiment as described above.

As described above, the method for mapping the synchronization signal tothe subcarrier of the frequency domain has the advantage that a repeatpattern is provided in one OFDM symbol of the time domain. That is, asdescribed above, if the sequence of the synchronization signal is mappedand an IFFT is performed with respect to the sequence, the time-domainsignal has a repeat pattern as much as the ratio of the maximumsubcarrier spacing to the subcarrier spacing of the synchronizationsignal currently used in the system in one OFDM symbol period. Forexample, since the synchronization signal sequence is mapped every foursubcarriers in the synchronization signal having 15 kHz subcarrierspacing, a pattern occurs, in which four equal signals “A” 670 arerepeated in a time corresponding to one OFDM symbol period 660, in atime-domain signal generated by performing the IFFT. The time-domainsignal “A” 670 is a signal that is equal to the synchronization signalof 60 KHz subcarrier spacing using the same synchronization signalsequence in the time domain. Further, since the synchronization signalsequence is mapped every two subcarriers in the synchronization signalhaving 30 kHz subcarrier spacing, a pattern occurs, in which two equalsignals “A” 670 are repeated in a time corresponding to one OFDM symbolperiod 660, in the time domain in which the IFFT is performed. Thetime-domain signal “A” 670 is a signal that is equal to thesynchronization signal of 60 KHz subcarrier spacing using the samesynchronization signal sequence in the time domain. Accordingly, inperforming initial synchronization using the synchronization signaltransmitted by the base station, the terminal may performcross-correlation using the synchronization signal of 60 KHz subcarrierspacing regardless of what subcarrier spacing the base station transmitsthe synchronization signal with.

As described above, the repeat pattern in the time domain of thesynchronization signal can provide many advantages in implementing areceiver of the terminal. First, in case of using the samesynchronization signal sequence d(k), the same time-domain pattern “A”670 occurs regardless of the subcarrier spacing, and thus from theviewpoint of the terminal, it is advantageous that the signal can bedetected using the same signal detector regardless of the subcarrierspacing used for the synchronization signal. Further, it is advantageousthat the terminal can detect the subcarrier spacing used for thesynchronization signal using the repeat pattern in the time domain.

According to the method for mapping the sequence for the synchronizationsignal to the subcarrier according to an embodiment of the presentdisclosure, various combinations of various subcarrier spacing set maybe possible. If 17.5 kHz, 35 kHz, and 70 kHz are considered as thesubcarrier spacings for the synchronization signal in the 5Gcommunication system considered in the present disclosure, the followingmapping rules may be used.

-   -   In the synchronization signal having 17.5 kHz subcarrier        spacing, the sequence used for the synchronization signal is        mapped to every fourth subcarrier among subcarriers allocated        for the synchronization signal, and a null (or “0”) is inserted        into the remaining subcarriers. That is, it is possible to apply        a comb-type structure in which the sequences used for the        synchronization signal are mapped to every four subcarriers.    -   In the synchronization signal having 35 kHz subcarrier spacing,        the sequence used for the synchronization signal is mapped to        every second subcarrier among subcarriers allocated for the        synchronization signal, and a null (or “0”) is inserted into the        remaining subcarriers. That is, it is possible to apply a        comb-type structure in which the sequences used for the        synchronization signal are mapped to every two subcarriers.    -   In the synchronization signal having 70 kHz subcarrier spacing,        the sequences used for the synchronization signal are mapped to        all subcarriers allocated for the synchronization signal. That        is, a structure is applied, in which sequences used for the        synchronization signal are mapped to all subcarriers without        considering the comb type.

Further, if 15 kHz, 30 kHz, 60 kHz, and 120 kHz are considered as thesubcarrier spacings for the synchronization signal in the 5Gcommunication system considered in the present disclosure, the followingmapping rules may be used.

-   -   In the synchronization signal having 15 kHz subcarrier spacing,        the sequence used for the synchronization signal is mapped to        every eighth subcarrier among subcarriers allocated for the        synchronization signal, and a null (or “0”) is inserted into the        remaining subcarriers. That is, it is possible to apply a        comb-type structure in which the sequences used for the        synchronization signal are mapped to every eight subcarriers.    -   In the synchronization signal having 30 kHz subcarrier spacing,        the sequence used for the synchronization signal is mapped to        every fourth subcarrier among subcarriers allocated for the        synchronization signal, and a null (or “0”) is inserted into the        remaining subcarriers. That is, it is possible to apply a        comb-type structure in which the sequences used for the        synchronization signal are mapped to every four subcarriers.    -   In the synchronization signal having 60 kHz subcarrier spacing,        the sequence used for the synchronization signal is mapped to        every second subcarrier among subcarriers allocated for the        synchronization signal, and a null (or “0”) is inserted into the        remaining subcarriers. That is, it is possible to apply a        comb-type structure in which the sequences used for the        synchronization signal are mapped to every two subcarriers.    -   In the synchronization signal having 120 kHz subcarrier spacing,        the sequences used for the synchronization signal are mapped to        all subcarriers allocated for the synchronization signal. That        is, a structure is applied, in which sequences used for the        synchronization signal are mapped to all subcarriers without        considering the comb type.

Further, if 15 kHz, 30 kHz, 60 kHz, and 120 kHz are considered as thesubcarrier spacings for the synchronization signal in the 5Gcommunication system considered in the present disclosure, the followingmapping rules may be used.

-   -   In the synchronization signal having 15 kHz subcarrier spacing,        the sequence used for the synchronization signal is mapped to        every second subcarrier among subcarriers allocated for the        synchronization signal, and a null (or “0”) is inserted into the        remaining subcarriers. That is, it is possible to apply a        comb-type structure in which the sequences used for the        synchronization signal are mapped to every two subcarriers.    -   In the synchronization signal having 30 kHz subcarrier spacing,        the sequences used for the synchronization signal are mapped to        all subcarriers allocated for the synchronization signal. That        is, a structure is applied, in which sequences used for the        synchronization signal are mapped to all subcarriers without        considering the comb type.    -   In the synchronization signal having 60 kHz subcarrier spacing,        the sequence used for the synchronization signal is mapped to        every second subcarrier among subcarriers allocated for the        synchronization signal, and a null (or “0”) is inserted into the        remaining subcarriers. That is, it is possible to apply a        comb-type structure in which the sequences used for the        synchronization signal are mapped to every two subcarriers.    -   In the synchronization signal having 120 kHz subcarrier spacing,        the sequences used for the synchronization signal are mapped to        all subcarriers allocated for the synchronization signal. That        is, a structure is applied, in which sequences used for the        synchronization signal are mapped to all subcarriers without        considering the comb type.

In the above-described case, the terminal can detect the synchronizationsignals having 15 kHz subcarrier spacing and 30 kHz subcarrier spacingthrough the same detector, and can detect the synchronization signalshaving 60 kHz subcarrier spacing and 120 kHz subcarrier spacing throughanother detector. Accordingly, the terminal performs an initial accesswith respect to the synchronization signal having 15 or 30 kHzsubcarrier spacing, and if the initial access has not succeeded, theterminal additionally performs the initial access with respect to thesynchronization signal having 60 kHz and 120 kHz subcarrier spacings todetect the subcarrier spacing that the base station supports for thesynchronization signal.

FIG. 7 is a diagram illustrating a method in which a terminal receiverdetects subcarrier spacings of a synchronization signal in case ofdifferently mapping synchronization sequences in accordance with thesubcarrier spacings used for the synchronization signal according to anembodiment of the present disclosure.

Referring to FIG. 7, terminal operations are illustrated with respect toan example 700 of a method for detecting a synchronization signal having15 kHz subcarrier spacing and an example 710 of a method for detecting asynchronization signal having 60 kHz subcarrier spacing, and even withrespect to 30 kHz, the terminal can operate with the same structure.Further, even in case of using a different subcarrier spacing set, theterminal may perform a similar detection operation.

If the maximum subcarrier spacing considered for the synchronizationsignal is 60 KHz, a synchronization signal 720 having 15 kHz subcarrierspacing has a structure in which a signal pattern “A” 730 is repeatedfour times in one OFDM symbol period in a time domain. In contrast, asynchronization signal 740 having 60 kHz subcarrier spacing has astructure in which the signal pattern “A” 730 is repeated once in oneOFDM symbol period. Accordingly, in case where the terminal detects areception signal using a detector 750 that can detect the signal “A”730, peaks 760 having four maximum values are detected in thesynchronization signal having 15 kHz subcarrier spacing, and in case ofa system having 60 kHz subcarrier spacing, a peak 760 having one maximumvalue can be detected. Accordingly, the terminal can detect the peaks760 occurring in a constant period using the signal “A” 730, and candetermine the subcarrier spacing used to transmit the synchronizationsignal through the number of peaks 760.

FIG. 8 is a flowchart illustrating a method in which a terminal detectssubcarrier spacings by performing an initial access using asynchronization structure proposed in the present disclosure accordingto an embodiment of the present disclosure.

Referring to FIG. 8, if the terminal starts its operation throughinitial power-on, it can detect the signal “A” of the synchronizationsignal at operation 800 corresponding to an initial access process.Here, the signal “A” means the synchronization signal of the time domaingenerated at the highest subcarrier spacing considered in the system. Ifit is assumed that the sequence of the synchronization signal differsfor each cell to indicate a different cell ID, the terminal shouldperform the detection on the assumption of a plurality of sequences “A”.If the terminal moves to operation 810 and a detector detects peaks ofthe signal “A”, the terminal moves to operation 829 to detect the numberof peaks of the signal “A”. Thereafter, the terminal moves to operation830 to discover the subcarrier spacing used for the synchronizationsignal in accordance with the number of detected peaks. For example, ifthe terminal detects the peaks four times through the detector detectingthe signal “A” in a state where the subcarrier spacings used for thesynchronization signal are 15 kHz, 30 KHz, and 60 KHz, the terminal mayassume that the synchronization signal being currently received has beentransmitted using 15 kHz subcarrier spacing. If the signal “A” is notdetected at operation 810, the terminal moves again to operation 800 todetect the signal “A” of the synchronization signal.

The terminal should perform time and frequency synchronization and cellsearch through the synchronization signal in the initial access process,and should acquire important information related to systemconfiguration. For example, in LTE, the terminal may perform the timeand frequency synchronization and the cell search through PSS and SSS,and may receive a master information block (MIB) that is importantinformation of the system through a physical broadcast channel (PBCH)received thereafter. Further, the terminal may receive a systeminformation block (SIB) that is overall system information related tothe system configuration thereafter.

Even in the 5G communication system, in a similar manner to the LTE, theterminal that performs the initial access should be able to receive MIBand SIB through completion of the synchronization through thesynchronization signal. In this case, a method is proposed, in which thesubcarrier spacings used for the synchronization signal are used in thesame manner for physical channels for transmitting the MIB and the SIB.Further, the terminal can also discover time and frequency spacings of areference signal transmitted together for the purpose of channelestimation of the physical channels for transmitting the MIB and the SIBthrough the subcarrier spacings of the synchronization signal.Accordingly, if the terminal detects the subcarrier spacings through thesynchronization signal, it may perform a reception operation on theassumption that the same subcarrier spacing can be used in the samemanner to receive the MIB and the SIB.

Further, in the present disclosure, a case where subcarrier spacingsthat are different from the subcarrier spacings used by the base stationfor the synchronization signal transmission are used for the physicalchannels for transmitting the MIB and the SIB. In this case, in orderfor the terminal having received the synchronization signal to properlyreceive the physical channel for transmitting the MIB and the physicalchannel for transmitting the SIB, there is a need for a method in whichthe base station notifies the terminal of the subcarrier spacing of thephysical channel for transmitting the MIB and the subcarrier spacing ofthe physical channel for transmitting the SIB.

In order for the terminal having detected the synchronization signal todiscover the subcarrier spacing of the physical channel for transmittingthe MIB, the base station may map the sequence of a specificsynchronization signal to the subcarrier spacing of the physical channelof the MIB. In case where the subcarrier spacing information fortransmitting the MIB is mapped to the specific sequence of thesynchronization signal, the terminal may receive the MIB using thesubcarrier spacing mapped to the corresponding sequence after detectingthe corresponding sequence. For example, if it is designated thatsequence #1 used for the synchronization signal means 15 kHz subcarrierspacing for the MIB transmission and sequence #2 means 30 kHz subcarrierspacing for the MIB transmission, and if the terminal detects sequence#2 from the synchronization signal, the terminal may assume 30 kHz asthe subcarrier spacing in receiving the physical channel including theMIB. Accordingly, the terminal attempts to receive the MIB on theassumption that the MIB is transmitted using the detected subcarrierspacing based on the synchronization signal sequence after detecting thesynchronization signal.

Further, in order for the terminal having received the synchronizationsignal and the MIB to discover the subcarrier spacing of the physicalchannel for transmitting the SIB, a method may be considered, in whichthe base station configures subcarrier spacing information of thephysical channel for transmitting the SIB to the terminal. The SIB maybe divided into several SIBs including information to be transmitted.For example, the base station may divide the system information to betransmitted to the terminals into SIB1 to SIBx (here, x means a certainnumeral) to be transmitted. For example, after the terminal receives theMIB, the base station may transmit important information related tosystem connection, which the terminal should first acquire afterreceiving the MIB, through SIB1, and may transmit information related toa random access of the terminal through SIB2.

On the assumption of the above-described case, a method for configuringthe subcarrier spacing of SIB1, which the terminal should first receiveafter acquiring the MIB, through the MIB may be proposed. In this case,one field including a predetermined number of bits may be included inthe MIB in order to configure the subcarrier spacing of SIB 1. Afterreceiving the MIB, the terminal may acquire the field for configuringthe subcarrier spacing of the physical channel for transmitting SIB1 inthe corresponding MIB, and may receive SIB1 using the correspondingsubcarrier spacing. It is proposed to configure the subcarrier spacingof the physical channel for transmitting SIBx that the terminal shouldreceive after SIB1 through SIB1. For this, a plurality of fieldsincluding a predetermined number of bits are included in SIB1, and theterminal may receive SIB1 and may acquire the field for transferring theinformation of the subcarrier spacing of SIBx. Thereafter, in receivingthe physical channel of the corresponding SIBx, the terminal may receiveSIBx using the subcarrier spacing information of SIBx configured in SIB1.

Further, in the present disclosure, it may be considered that theterminal receives a downlink signal or transmits an uplink signal usinga downlink synchronization signal and a subcarrier spacing that isdifferent from the subcarrier spacing used for the physical channel fortransmitting MIB and SIB. Since the base station does not know thesituation of the terminal existing in the cell, it is unable to transmita signal using the subcarrier spacing that is considered as optimum foreach terminal, and is unable to receive a signal transmitted by theterminal using another subcarrier spacing. In contrast, the terminal maymeasure the multi-path delay spread and Doppler spread in considerationof the channel situation and moving speed of the terminal, and mayrequest the base station to use the subcarrier spacing suitable for theterminal to receive the downlink signal and the subcarrier spacingsuitable to transmit the uplink signal.

Accordingly, in the present disclosure, a method by the terminal forrequesting subcarrier spacings for downlink signal reception and uplinksignal transmission using a random access preamble is proposed. In orderto request the downlink and uplink subcarrier spacings desired by theterminal itself, the terminal may use the random access preamble in aninitial access state. The terminal may request the subcarrier spacingfrom the base station by randomly selecting and transmitting the randomaccess preamble from a random access preamble set that is mapped to thesubcarrier spacing in a one-to-one manner among the whole random accesspreambles. That is, the base station may configure one set by tying aplurality of preambles, and the whole random access preambles may becomposed of a plurality of preamble sets. In this case, each of therespective preamble sets may be used to indicate one subcarrier spacing.

The base station may configure the random access preamble setinformation and related subcarrier spacing information to the terminalsin the cell in a cell-common manner. For example, if it is assumed thatthere are 64 random access preambles in total, preambles having indexes0 to 31 may constitute one preamble set, and preambles having theremaining indexes may constitute a second set. The first set may be usedto request 15 kHz subcarrier spacing, and the second set may be used torequest 30 kHz subcarrier spacing. In this case, if the terminaltransmits the random access preamble using the preamble having index #0and the base station detects the corresponding sequence, the basestation may analogize that the corresponding terminal has requested 15kHz as the subcarrier spacing.

Further, if the terminal transmits the preamble requesting a specificsubcarrier spacing in the random access process, it attempts downlinksignal reception on the assumption that a random access response isreceived through the use of the requested subcarrier spacing inreceiving the random access response thereafter. Further, the terminalhaving succeeded in reception of the random access response transmitsthe signal on the assumption that it is possible to transmit the uplinksignal through the subcarrier spacing requested through the randomaccess preamble even if there is no special configuration in relation tothe subcarrier spacing thereafter.

FIGS. 9, 10A and 10B are block diagrams illustrating a transmission unitof a base station and a reception unit of a terminal for performingembodiments of the present disclosure. The transmission unit of the basestation and the reception unit of the terminal should operate inaccordance with initial access method and device of a 5G communicationsystem proposed in the above-described embodiments.

FIG. 9 is a block diagram illustrating the internal structure of a basestation transmission unit according to an embodiment of the presentdisclosure. Referring to FIG. 9, the transmission unit of the basestation according to the present disclosure is composed of asynchronization signal sequence generator 900, a subcarrier mapper 910,a null inserter 920, an OFDM signal generator 930, an RF unit 940, andan antenna. Further, the base station according to the presentdisclosure may be composed of a controller and a transceiver includingthe transmission unit, and the controller may control the transceiver toperform embodiments of the present disclosure. The synchronizationsignal sequence generator 900 generates sequences of a synchronizationsignal for the terminal to discover the corresponding cell number inaccordance with an ID of the cell managed by the corresponding basestation. The synchronization signal sequences generated by the sequencegenerator 900 are input to the subcarrier mapper 910. Further, the nullinserter 920 generates and inputs symbols having a value of “0” to thesubcarrier mapper 910. The subcarrier mapper 910 properly maps thesynchronization signal sequences and the null to the subcarriers inaccordance with the subcarriers used for the synchronization signal inthe subcarrier spacing set considered by the base station. The OFDMsignal generator 930 generates a time-domain OFDM signal using thesubcarriers mapped through the subcarrier mapper 910, and transfers thegenerated OFDM signal to the RF unit 940. The RF unit 940 converts abaseband signal into a transition band signal, and transfers theconverted transition band signal to the antenna to transmit thecorresponding signal through the antenna.

FIG. 10A is a block diagram illustrating the internal structure of aterminal reception unit according to an embodiment of the presentdisclosure. Referring to FIG. 10A, a terminal transmission unit iscomposed of an RF unit 1000, a signal “A” detector 1010, a peak detector1020, a subcarrier spacing detector 1030, and a controller 1040.Further, the terminal according to the present disclosure may becomposed of a transceiver including the terminal transmission unit andthe controller 1040, and the controller may control the transceiver toperform embodiments of the present disclosure. The RF unit 1000 performsa role of converting a received transition band signal into a basebandsignal. The converted baseband signal is input to the signal “A”detector 1010 that is a detector detecting a synchronization signal forthe signal received through the signal “A” detector 1010. As exemplifiedin FIG. 7, the signal “A” is a time-domain signal of the synchronizationsignal generated at the largest subcarrier spacing supported by the basestation, and matched filtering is performed with respect to thecorresponding signal. The matched filtering output from the signal “A”detector 1010 is transferred to the peak detector 1020 to detect peaksthereof, and the number of detected peaks is transferred to thesubcarrier spacing detector 1030. The subcarrier spacing detector mayestimate the subcarrier spacing in accordance with the number ofdetected peaks. The controller 1040 may control the RF unit 1000, thesignal “A” detector 1010, the peak detector 1020, and the subcarrierspacing detector 1030 constituting the terminal.

FIG. 10B is a block diagram illustrating the configuration of a basestation according to an embodiment of the present disclosure. Referringto FIG. 10B, the base station according to the present disclosure may becomposed of a transceiver 1050 and a controller 1060, and the controller1060 may control the transceiver 1050 to transmit and receive thesignal. Specifically, according to an embodiment of the presentdisclosure, the controller may generate at least one of asynchronization signal, MIB, and SIB, and may transmit at least one ofthe synchronization signal, MIB, and SIB using the transceiver.

Second Embodiment

In general, a mobile communication system has been developed to providea voice service while securing user activity. However, the mobilecommunication system has gradually extended its domain up to dataservice providing in addition to the voice service, and at present, ithas been developed up to the level capable of providing a high-speeddata service. However, since resource shortage phenomenon occurs underthe current mobile communication system and users require higher-speedservices, there has been a need for a more developed mobilecommunication system.

As one system that has been developed as the next-generation mobilecommunication system to meet such a need, standardization work for longterm evolution (LTE) is in progress in the 3rd Generation PartnershipProject (3GPP). The LTE is a technology implementing high-speed packetbased communication having a transmission speed of about 100 Mbps atmaximum. For this, various schemes have been discussed, for example, ascheme for reducing the number of nodes located on a communication paththrough simplification of a network structure and a scheme for maximallyapproaching radio protocols to radio channels.

The LTE system adopts a hybrid automatic repeat request (HARQ) scheme inwhich a physical layer retransmits corresponding data if decodingfailure occurs during initial transmission. According to the HARQscheme, a receiver transmits information (negative acknowledgement(NACK)) for notifying a transmitter of decoding failure if the receiveris unable to accurately decode data, and the transmitter may make aphysical layer retransmit the corresponding data. The receiver maycombine the data that is retransmitted by the transmitter with theprevious data of which the decoding has failed to heighten the datareception performance. Further, if the receiver has accurately decodedthe data, the receiver may transmit information (acknowledgement (ACK))for notifying the transmitter of decoding success, and thus thetransmitter can transmit new data.

FIG. 11 is a diagram illustrating the basic structure of atime-frequency domain that is a radio resource region in which data or acontrol channel is transmitted in a downlink in an LTE system.

Referring to FIG. 1, a horizontal axis represents a time domain, and avertical axis represents a frequency domain. In the time domain, theminimum transmission unit is an OFDM symbol, and N_(symb) OFDM symbols1150 constitute one slot 1120, and two gathered slots constitute onesubframe 1110. The length of the slot is 0.5 ms, and the length of thesubframe is 1.0 ms. Further, a radio frame 1100 is a time-domain unitthat is composed of 10 subframes. In the frequency domain, the minimumtransmission unit is a subcarrier, and the transmission bandwidth of thewhole system is composed of N_(BW) subcarriers 1170 in total.

In the time-frequency domain, the basic unit of resources is a resourceelement (RE) 1140 that may be expressed by an OFDM symbol index and asubcarrier index. A resource block (RB) (or physical resource block(PRB)) 1130 is defined by N_(symb) successive OFDM symbols 1150 in thetime domain and N_(RB) successive subcarriers 1160 in the frequencydomain. Accordingly, one RB 1130 is composed of N_(symb)×N_(RB) REs1140. In general, the minimum transmission unit of data is the RB unit,and in the LTE system, N_(symb)=7, N_(RB)=12, and N_(BW) and N_(RB) arein proportion to the bandwidth of the system transmission band.

The data rate is increased in proportion to the number of RBs that arescheduled in the terminal. The LTE system may define and operate 6transmission bandwidths. In case of a frequency division duplex (FDD)system that operates to discriminate a downlink and an uplink by meansof the frequency, the downlink transmission bandwidth and the uplinktransmission bandwidth may differ from each other. A channel bandwidthrepresents an RF bandwidth that corresponds to the system transmissionbandwidth. Table 1 below presents the corresponding relationship betweenthe system transmission bandwidth and the channel bandwidth defined inthe LTE system. For example, the LTE system having 10 MHz channelbandwidth has the transmission bandwidth that is composed of 50 RBs.

TABLE 1 Channel bandwidth BWChannel [MHz] 1.4 3 5 10 15 20 Transmission6 15 25 50 75 100 bandwidth configuration NRB

Downlink control information is transmitted within initial N OFDMsymbols in the subframe. In general, N={1, 2, 3}. Accordingly, inaccordance with the amount of control information to be transmitted tothe current subframe, the value N is varied for each subframe. Thecontrol information includes a control channel transmission intervalindicator indicating how many OFDM symbols the control information istransmitted through, scheduling information on downlink data or uplinkdata, and HARQ ACK/NACK signal.

In the LTE system, the scheduling information on the downlink data orthe uplink data is transferred from the base station to the terminalthrough downlink control information (DCI). The uplink (UL) means aradio link on which the terminal transmits data or a control signal tothe base station, and the downlink (DL) means a radio link on which thebase station transmits data or a control signal to the terminal. The DCIis defined in various formats, and the respective formats are applieddepending on whether the DCI is scheduling information on uplink data(UL grant) or scheduling information on downlink data (DL grant),whether the DCI is a compact DCI having a small size of the controlinformation, whether spatial multiplexing using multiple antennas isapplied, and whether the DCI is a DCI for power control. For example,DCI format 1 that is the scheduling control information on the downlinkdata (DL grant) is configured to include at least the following controlinformation.

-   -   Resource allocation type 0/1 flag: This notifies of whether a        resource allocation scheme is of type 0 or type 1. The type 0        allocates resources in the unit of a resource block group (RBG)        through application of a bitmap scheme. In the LTE system, the        basic unit of scheduling is an RB that is expressed as time and        frequency domain resource, and the RBG is composed of a        plurality of RBs, and becomes the basic unit of scheduling in        the type 0 scheme. The type 1 allocates a specific RB in the        RBG.    -   Resource block assignment: This notifies of an RB that is        allocated for data transmission. An expressed resource is        determined in accordance with the system bandwidth and the        resource allocation scheme.    -   Modulation and coding scheme (MCS): This notifies of a        modulation scheme that is used for data transmission and the        size of a transport block that is data to be transmitted.    -   HARQ process number: This notifies of a process number of a        HARQ.    -   New data indicator: This notifies of whether transmission is        HARQ initial transmission or retransmission.    -   Redundancy version: This notifies of a redundancy version of a        HARQ.    -   Transmission power control (TCP) command for a physical uplink        control channel (PUCCH): This notifies of a transmission power        control command for a PUCCH that is an uplink control channel.

The DCI passes through a channel coding and modulation process, and istransmitted on a physical downlink control channel (PDCCH) that is adownlink physical control channel or enhanced PDCCH (EPDCCH).Hereinafter, the DCI transmission on the PDCCH may be mixedly used withthe PDCCH transmission. This may also be applied to other similarchannels.

In general, the DCI is independently channel-coded with respect torespective terminals, and is configured as an independent PDCCH to betransmitted. In the time domain, the PDCCH is mapped during the controlchannel transmission interval to be transmitted. The frequency domainmapping location of the PDCCH is determined by an Identifier (ID) ofeach terminal, and is spread over the whole system transmission band.

The downlink data is transmitted on a physical downlink shared channel(PDSCH) that is a physical downlink data channel. The PDSCH istransmitted after the control channel transmission period, andscheduling information, such as a detailed mapping location in thefrequency domain and the modulation scheme, is notified by the DCItransmitted through the PDCCH. Hereinafter, downlink data transmissionon the PDSCH may be mixedly used with the PDSCH transmission. This mayalso be applied to other similar channels.

Through an MCS composed of 5 bits among the control informationconstituting the DCI, the base station notifies the terminal of themodulation scheme that is applied to the PDSCH to be transmitted to theterminal and a transport block size (TBS) of data to be transmitted. TheTBS corresponds to the data size before a channel coding for errorcorrection is applied to the data (TB), which the base station intendsto transmit.

The modulation scheme supported in the LTE system is quadrature phaseshift keying (QPSK), 16 quadrature amplitude modulation (16QAM), or64QAM, and respective modulation orders Q_(m) correspond to 2, 4, and 6.That is, in case of the QPSK modulation, 2 bits per symbol may betransmitted, and in case of the 16QAM modulation, 4 bits per symbol maybe transmitted. Further, in case of the 64QAM modulation, 6 bits persymbol may be transmitted.

In 3GPP LTE Release 10 (Rel-10), as compared with LTE Rel-8, bandwidthextension technology has been adopted to support higher datatransmission rate. The above-described technology called bandwidthextension or carrier aggregation (CA) may increase the data transmissionrate as much as the extended band as compared with an LTE Rel-8 terminaltransmitting data in one band. Each of the respective bands is called acomponent carrier (CC), and the LTE Rel-8 terminal is prescribed to haveone component carrier with respect to the downlink or the uplink.Further, the downlink component carrier and the uplink component carrierconnected through system information block (SIB)-2 are tied to be calleda cell. The SIB-2 connection relationship between the downlink componentcarrier and the uplink component carrier is transmitted as a systemsignal or a higher signal. The terminal supporting the CA may receivethe downlink data and may transmit the uplink data through a pluralityof serving cells.

In Rel-10, if the base station is in a situation where it is difficultfor the base station to transmit the PDCCH to a specific terminal in aspecific serving cell, it may transmit the PDCCH in another servingcell, and may configure a carrier indicator field (CIF) as a fieldnotifying that the corresponding PDCCH indicates data transmission on aPDSCH of another serving cell or a physical uplink shared channel(PUSCH). The CIF may be configured to the terminal supporting the CA.The CIF is determined to indicate another serving cell through additionof 3 bits to the DCI transmitted in the specific serving cell, and theCIF is included only in case of performing cross carrier scheduling. Ifthe CIF is not included, the cross carrier scheduling is not performed.If the CIF is included in downlink assignment information (it may beunderstood as DL assignment or DL grant), the CIF is defined to indicatea serving cell to which the PDSCH that is scheduled by the downlinkassignment information is to be transmitted and to indicate a servingcell to which the PUSCH that is scheduled by the uplink assignmentinformation is to be transmitted.

As described above, in LTE-10, the carrier aggregation that is thebandwidth extension technology is defined, and a plurality of servingcells may be configured to the terminal. Further, the terminalperiodically or aperiodically transmits channel information on theplurality of serving cells to the base station for data scheduling ofthe base station. Further, the base station schedules and transmits datafor each carrier, and the terminal transmits A/N feedback for the datatransmitted for each carrier. In LTE Rel-10, it is designed to transmitthe A/N feedback of 21 bits at maximum, and if the transmission of theA/N feedback overlaps the transmission of the channel information on onesubframe, it is designed to transmit the A/N feedback and to discard thechannel information. In LTE Rel-11, it is designed to transmit the A/Nfeedback of 22 bits at maximum and channel information of one cell usingPUCCH format 3 on the transmission resource of the PUCCH format 3through multiplexing of the A/N feedback and the channel information ofone cell.

In LTE-13, maximally 32 serving cell configuration scenarios areassumed, and the concept of extending the number of serving cellsmaximally up to 32 using not only licensed bands but also unlicensedbands has been introduced. Further, in consideration of the situationwhere the number of licensed bands, such as LTE frequency, is limited,standardization of the technology to provide an LTE service in anunlicensed band, such as 5 GHz band, has been completed, and this iscalled a licensed assisted access (LAA). In the LAA, it is supportedthat an LTE cell that is a licensed band is operated as a primary cell(P cell) and an LAA cell that is an unlicensed band is operated as asecondary cell (S cell) through application of the carrier aggregationtechnology in the LTE. Accordingly, feedback generated in the LAA cellthat is an S cell like the LTE should be transmitted only from the Pcell, and in the LAA cell, downlink subframes and uplink subframes canbe freely applied. Unless separately described in the description, LTEmay be called to include all LTE evolved technology, such as LTE-A andLAA.

On the other hand, new radio access technology (NR) that is a beyond LTEcommunication system, that is, 5G wireless cellular communication system(in the description, referred to as “5G”), is required to freely reflectvarious requirements of users and service providers, and thus servicesthat satisfy the various requirements should be supported.

Accordingly, 5G may be defined as technology to satisfy the requirementsselected for respective 5G oriented services, such as enhanced mobilebroadband (hereinafter, “eMBB”), massive machine type communication(hereinafter, “mMTC”), and ultra-reliable and low latency communications(hereinafter, “URLLC”), among requirements, such as 20 Gbps of theterminal maximum transmission speed, 500 km/h of the terminal maximumspeed, 0.5 ms of the maximum delay time, and 1,000,000 UE/km² of theterminal connection density.

For example, in order to provide eMBB in 5G, from the viewpoint of onebase station, it is required to provide 20 Gbps of terminal maximumtransmission speed through downlink and to provide 10 Gbps of terminalmaximum transmission speed through uplink. At the same time, bodilysensed terminal average transmission speed should be increased. In orderto satisfy the requirements as described above, there is a need forimprovement of transmission/reception technology including more improvedmultiple-input multiple-output (MIMO) transmission technology.

Also, in order to support an application service, such as Internet ofthings (IoT) in 5G, an mMTC is considered. In order to efficientlyprovide the IoT using the mMTC, requirements of massive terminalconnection support, terminal coverage improvement, improved batterytime, and terminal cost reduction should be satisfied. Since the IoT isattached to several sensors and various machines to providecommunication functions, it is necessary to support a large number ofterminals (e.g., 1,000,000 UE/km²) in the cell. Further, since there ishigh possibility that due to the service characteristics, the terminalis located in a shaded area, such as underground of a building or anarea where the cell is not covered, a wider coverage than the coverageprovided by the eMBB is necessary. There is a high possibility that themMTC is configured as a cheap terminal, and since it is difficult tofrequently exchange the battery of the terminal, a very long batterylife time is required.

Last, in case of the URLLC that is a cellular based wirelesscommunication used for a specific purpose, it is a service used forremote control of a robot or machine device, industry automation,unmanned aerial vehicle, remote health care, and emergency situationalarm, and thus it is necessary to provide communication having lowlatency and ultra-reliability. For example, the URLLC should satisfy themaximum delay time that is shorter than 0.5 ms, and also should satisfya packet error rate that is equal to or lower than 10⁻⁵. Accordingly,for the URLLC, transmit time interval (TTI) that is shorter than that ofa 5G service, such as eMBB, should be provided, and design requirementin which wide resources should be allocated in the frequency band shouldbe satisfied. In the present disclosure, although “subframe” is usedwith respect to the transmit time interval, “subframe”, “slot”, “minislot”, and “TTI” may have the same meaning in all.

Services considered in the 5G wireless cellular communication system asdescribed above should be provided as one framework. That is, forefficient resource management and control, it is preferable thatrespective services are not independently operated, but are integrallycontrolled and transmitted as one system.

FIG. 12 is a diagram illustrating an example in which services beingconsidered in 5G are multiplexed through one system to be transmitted.

In FIG. 12, frequency-time resource 1200 used by 5G may be composed of afrequency axis 1210 and a time axis 1220. In FIG. 12, it is exemplifiedthat eMBB 1230, mMTC 1240, and URLLC 1250 are operated by a 5G basestation in one framework. Further, as a service that may be additionallyconsidered in 5G, enhanced mobile broadcast/multicast service (eMBMS)1260 for providing a cellular-based broadcasting service may beconsidered. The services being considered in 5G, such as eMBB 1230, mMTC1240, URLLC 1250, and eMBMS 1260, may be multiplexed to be transmittedthrough time-division multiplexing (TDM) or frequency divisionmultiplexing (FDM) in one system frequency bandwidth operated in 5G, andspatial division multiplexing may also be considered.

In case of eMBB 1230, it is preferable to occupy and transmit themaximum frequency bandwidth at a certain specific time to provideincreased data transmission speed as described above. Accordingly, inthe service of eMBB 1230, it is preferable that the service is TDMmultiplexed with other services in the system transmission bandwidth1200 to be transmitted, and it is also preferable that the service isFDM-multiplexed with other services in the system transmission bandwidthas needed by other services.

In case of mMTC 1240, in order to secure a wide coverage in contrastwith other services, an increased transmission interval is required, andthe coverage can be secured through repeated transmission of the samepacket in the transmission interval. At the same time, in order toreduce terminal complexity and terminal costs, the transmissionbandwidth that can be received by the terminal is limited. Inconsideration of such requirements, it is preferable that mMTC 1240 isFDM-multiplexed with other services in the 5G transmission systembandwidth 1200 to be transmitted.

In order to satisfy ultra-low latency requirements requested by theservice, it is preferable that URLLC 1250 has a short transmit timeinterval as compared with other services. At the same time, in order tosatisfy ultra-reliable requirements, it is necessary to have a lowcoding rate, and thus it is preferable to have a wide bandwidth on thefrequency side. In consideration of the requirements of the URLLC 1250,it is preferable that the URLLC 1250 is TDM-multiplexed with otherservices in the 5G transmission system bandwidth 1200.

In order to satisfy the requirements required by the respectiveservices, the respective services as described above may have differenttransmission/reception techniques and transmission/reception parameters.For example, the respective services may have different numerologies inaccordance with the respective service requirements. Here, thenumerology includes a cyclic prefix (CP) length, subcarrier spacing,OFDM symbol length, and transmit interval length (TTI) in acommunication system based on orthogonal frequency division multiplexing(OFDM) or orthogonal frequency division multiple access (OFDMA).

As an example in which the services have different numerologies, eMBMS1260 may have a long CP length as compared with other services. SinceeMBMS transmits a broadcasting-based upper traffic, the same data can betransmitted in all cells. In this case, as seen from the terminal, ifsignals received from a plurality of cells arrive within the CP length,the terminal can receive and decode all the signals, and thus a singlefrequency network (SFN) diversity gain can be obtained. Accordingly,even the terminal located on the cell boundary can receive thebroadcasting information without coverage limits. However, if the CPlength is relatively long as compared with that of other services, wastedue to a CP overhead occurs. At the same time, a long OFDM symbol lengthas compared with that of other services is required, and thus a narrowersubcarrier interval as compared with that of other services is required.

Further, as an example in which different numerologies are used betweenservices in 5G, in case of the URLLC, since a short TTI is required ascompared with that of other services, a shorter OFDM symbol length isrequired, and at the same time, a wider subcarrier spacing may berequired.

As described above, in order to satisfy various requirements in 5G,requirements for various services are described, and requirements forthe representatively considered services have been described.

The frequency range in which 5G is considered to be operated reachesseveral GHz to several tens of GHz, and in the several tens of GHz bandhaving low frequency, a frequency division duplex (FDD) system ispreferred rather than a time division duplex (TDD) system, and in theseveral tens of GHz band having high frequency, it is considered thatthe TDD system is more suitable than the FDD system. However, incontrast with the FDD that seamlessly provides uplink/downlinktransmission resources through putting of separate frequencies for theuplink/downlink transmission, the TDD should support all theuplink/downlink transmission at one frequency, and in accordance withtime, it provides only the uplink resource or downlink resource. If itis assumed that uplink or downlink transmission of the URLLC service isnecessary in the TDD system, it becomes difficult to satisfy theultra-low latency requirements required by the URLLC due to the delay upto the time when the uplink or downlink resource appears. Accordingly,in case of the TDD, in order to satisfy the ultra-low latencyrequirements of the URLLC, there is a need for a method for dynamicallychanging the subframe uplink or downlink depending on whether the URLLCdata corresponds to uplink transmission or downlink transmission.

On the other hand, even in case of multiplexing services andtechnologies for forward 5G phase 2 or beyond 5G into 5G operatingfrequencies in 5G, it is required to provide the 5G phase 2 or beyond 5Gtechnology and services so that there is no backward compatibilityproblem in operating the 5G. The requirement conditions are calledforward compatibility, and technologies for satisfying the forwardcompatibility should be considered in case of designing the 5G.

In the initial LTE standardization stage, consideration of the forwardcompatibility is unprepared, and thus there may be a limit in providinga new service in the LTE framework. For example, in case of the enhancedmachine type communication (eMTC) applied in LTE release-13,communication becomes possible only in the frequency band correspondingto 1.4 MHz regardless of the system bandwidth provided by a serving cellin order to reduce the terminal costs through reduction of the terminalcomplexity. Accordingly, since the terminal that supports the eMTCcannot receive the PDCCH transmitted over the full band of the existingsystem bandwidth, a signal is unable to be received at the time intervalwhen the PDCCH is transmitted. Accordingly, the 5G communication systemshould be designed so that services considered after the 5Gcommunication system efficiently coexists with the 5G communicationsystem. In the 5G communication system, for forward compatibility,resources should be able to be freely allocated so that services to beconsidered forward can be freely transmitted in the time-frequencyresource region supported in the 5G communication system. Accordingly,in order to support the forward compatibility in the 5G communicationsystem, there is a need for a method for freely allocatingtime-frequency resources.

In the 5G communication system, one TTI may be defined as one slot, andmay be composed of 14 OFDM symbols or 7 OFDM symbols. Accordingly, incase of 15 kHz subcarrier spacing, one slot has a length of 1 or 0.5 ms.Further, in the 5G, for emergency transmission and transmission in anunlicensed band, one TTI may be defined as one mini-slot or sub-slot,and one mini-slot may have one to ((the number of OFDM symbols of aslot) −1) OFDM symbols. For example, if the length of one slot is 14OFDM symbols, the length of a mini-slot may be determined as one of 1 to13 OFDM symbols.

Further, instead of separately defining the terms “slot” and“mini-slot”, the TTI may be defined only by the slot. Accordingly, thelength of one slot may be differently configured for each terminal, andone slot may have one to (the number of OFDM symbols in a slot) OFDMsymbols. The length of the slot or mini-slot may be defined in thestandards, or may be transmitted to the terminal through a higher signalor system information. The slot or mini-slot may be defined to havevarious transmission formats, and may be classified into the followingformats.

DL only slot or full DL slot: The DL only slot is composed of only DLinterval, and only DL transmission is supported.

-   -   DL centric slot: The DL centric slot is composed of a DL        interval, a GP, and a UL interval, and the number of OFDM        symbols in the DL interval is larger than the number of OFDM        symbols in the UL interval.    -   UL centric slot: The UL centric slot is composed of a DL        interval, a GP, and a UL interval, and the number of OFDM        symbols in the DL interval is smaller than the number of OFDM        symbols in the UL interval.    -   UL only slot or full UL slot: The UL only slot is composed of        only a UL interval, and only UL transmission is supported.

Although only the slot format is classified as described above, themini-slot can also be divided in the same classification method. Thatis, the mini-slot may also be divided into a DL only mini-slot, a DLcentric mini-slot, a UL centric mini-slot, and a UL only mini-slot.

In the present disclosure, the slot formats as described above aredescribed as the term “subframes” having the same meaning.

Hereinafter, preferred embodiments of the present disclosure will bedescribed in detail with reference to the accompanying drawings. In theaccompanying drawings, it is to be noted that the same referencenumerals are used for the same constituent elements. Further, a detaileddescription of known functions and configurations will be omitted if itobscures the subject matter of the present disclosure.

Further, in describing embodiments of the present disclosure in detail,LTE and 5G systems will be the main subject. However, the main subjectof the present disclosure may also be applied to other communicationsystems having similar technical backgrounds or channel types throughslight modifications thereof in a range that does not greatly deviatefrom the scope of the present disclosure through the judgment of thoseskilled in the art to which the present disclosure pertains.

Hereinafter, a 5G communication system in which 5G cells operate in astand-alone manner or a 5G communication system in which 5G cells arecombined with other stand-alone 5G cells through dual connectivity orcarrier aggregation to operate in a non-stand-alone manner will bedescribed.

FIGS. 13A and 13B are diagrams illustrating first and second embodimentsof a communication system to which the present disclosure is applied.Schemes proposed in the present disclosure can be applied to the systemof FIG. 13A and the system of FIG. 13B in all.

Referring to FIG. 13A, a case where a 5G cell 1310 operates in astand-alone manner in one base station 1300 in a network is illustrated.A terminal 1320 is a 5G capable terminal having a 5Gtransmission/reception module. The terminal 1320 acquiressynchronization through a synchronization signal transmitted from a 5Gstand-alone cell 1310, receives system information, and then attempts arandom access to the 5G base station 1300. The terminal 1320 transmitsand receives data through the 5G cell 1310 after completing an RRCconnection with the 5G base station 1300. In this case, a duplex type ofthe 5G cell 1310 is not limited. In the system of FIG. 13A, the 5G cellmay be provided with a plurality of serving cells.

Referring to FIG. 13B, a case where a 5G stand-alone base station 1330and a 5G non-stand-alone base station 1340 for increasing the data rateare installed is illustrated. The terminal 1360 is a 5G capable terminalhaving a 5G transmission/reception module for a plurality of basestations to perform 5G communication. The terminal 1360 acquiressynchronization through a synchronization signal transmitted from the 5Gstand-alone base station 1330, receives system information, and thenattempts a random access to the 5G stand-alone base station 1330. Theterminal 1360 additionally configures a 5G non-stand-alone cell 1370after completing RRC connection with the 5G stand-alone base station1330, and transmits and receives data through the 5G stand-alone basestation 1330 or the 5G non-stand-alone base station 1340. In this case,the duplex type of the 5G stand-alone base station 1330 or the 5Gnon-stand-alone base station 1340 is not limited, and it is assumed thatthe 5G stand-alone base station 1330 or the 5G non-stand-alone basestation 1340 are connected through an ideal backhaul network or anon-ideal backhaul network. Accordingly, in the case of having the idealbackhaul network 1350, rapid X2 communication between base stationsbecomes possible. In the system of FIG. 13B, the 5G cell may be providedwith a plurality of serving cells.

Next, in case of operating the TDD in the 5G communication system ofFIGS. 13A and 13B, a scheme will be described, in which a subframe (itcan be mixedly used with a slot) is divided into a plurality of types,and it is prevented to exceed the maximum delay time during signaltransmission/reception in consideration of a specific one of respectivesubframe types as a subframe that can be dynamically changed uplink anddownlink.

First, FIG. 14 is a diagram illustrating a first embodiment in which 5Gfor each subframe type is operated in TDD. Referring to FIG. 14, in caseof operating a 5G communication system in one TDD carrier, the subframetype is divided into a fixed subframe, an RRC subframe, and a dynamicsubframe, and the base station and the terminal may transmit and receivedata in a manner that they perform synchronization signal and systeminformation transmission and random access in the fixed subframe,perform additional system information transmission and additional randomaccess in the RRC subframe, and dynamically change the subframes tomatch the uplink/downlink data in the dynamic subframes.

First, the fixed subframe will be described. The fixed subframe may be asubframe determined as uplink or downlink subframe, or a subframe havinga part of a resource fixed as uplink or downlink resource in thesubframe. Referring to FIG. 14, TDD 1400 information (carrier frequency,frequency band (BW), and their location information) may be transmittedfrom a 5G base station to a 5G capable terminal, and the 5G capableterminal may obtain the above-described information throughsynchronization acquisition and essential system information receptionin the fixed subframe 1410. As described above, the resource fixeduplink or downlink may be composed of one or more OFDM symbols in thetime domain, and may be composed of one or more REs or PRBs in thefrequency domain. The location and the number of fixed subframes 1410are merely exemplary, and locations of other fixed subframes and thenumber of fixed subframes, or DL fixed subframes and UL fixed subframesmay be determined in advance through the standards. Further, they may beincluded in system information to be transmitted to the terminal.

The 5G capable terminal may attempt to acquire synchronization andessential system information from the DL fixed subframes, acquire randomaccess related information through the received essential systeminformation, and attempt the random access in the UL fixed subframes.Further, the 5G capable terminal may attempt to acquire synchronizationand essential system information from the time or frequency resourceprescribed in the standards, acquire information on the fixed subframesand random access related information through the received essentialsystem information, and attempt the random access in the UL fixedsubframes.

Next, RRC subframe 1420 will be described. It is preferable to determinethe minimum number of fixed subframes 1410 in the standards. This isbecause, if the number of fixed subframes 1410 becomes larger, it isrequired to take a delay time caused by the fixed subframes intoconsideration. If UL data transmission for URLLC is performed in the DLfixed subframe, it is required to delay URLLC UL data transmission untilan UL subframe appears, and in this case, it is difficult to satisfyultra-delay time requirements for URLLC. Accordingly, instead ofminimizing the number and the locations of fixed subframes 1410, it ispossible to make the base station configure the RRC subframe 1420through higher signal transmission in order to support servicespecialized system information transmission in accordance with thenumber of terminals in the cell and a random access command by the basestation. The terminal acquires the location and the number ofuplink/downlink subframes of the RRC subframe 1420 through the receptionof the higher signal, and performs decoding of downlink controlinformation only in the subframe having a downlink resource on which thedecoding of the downlink control information should be performed in theRRC subframe 1420 to reduce decoding complexity. The fixed subframe mayalso be included in the higher signal.

Specifically, if there is no information on the RRC subframe 1420 fromthe base station, the terminal does not attempt decoding of the downlinkcontrol information with respect to the uplink fixed subframe 1410, butattempts to decode the downlink control information only with respect tothe downlink fixed subframe 1410. The terminal determines the remainingsubframes excluding the fixed subframe 1410 as dynamic subframes 1430 inall, and attempts to decode the downlink control information for eachsubframe.

If the terminal receives the information on the RRC subframe 1420transmitted from the base station, it does not attempt decoding of thedownlink control information with respect to the uplink fixed subframe1410, but attempts to decode the downlink control information only withrespect to the downlink fixed subframe 1410. Next, the terminal does notattempt decoding of the downlink control information with respect to theuplink RRC subframe 1420, but attempts to decode the downlink controlinformation only with respect to the downlink RRC subframe 1420. Theterminal determines the remaining subframes excluding the fixed subframe1410 and the RRC subframe 1420 as dynamic subframes 1430 in all, andattempts to decode the downlink control information for each subframe.

Next, the dynamic subframe 1430 will be described. The dynamic subframe1430 may be a downlink subframe or may be an uplink subframe inaccordance with the base station scheduling. The terminal determineswhether the corresponding dynamic subframe 1430 is uplink or downlinksubframe through reception of the downlink control informationtransmitted by the base station, and performs downlink data receptionand uplink data transmission in accordance with the scheduling by thedetermined subframe and the decoded downlink control information.

If the terminal receives the downlink control information for thecorresponding subframe after acquiring information on the fixed subframeor RRC subframe, it may perform the following operation.

First, the terminal disregards reception of the downlink controlinformation, and performs an operation with respect to the fixedsubframe or the RRC subframe in accordance with previously acquiredinformation. That is, the terminal operates to maintain the UL/DLstructure or format structure for the fixed subframe or the RRCsubframe. In this case, it is advantageous that interference does notexert an influence on other terminals in the system.

Second, the terminal performs an operation with respect to thecorresponding subframe by updating the previously acquired informationthrough the newly received downlink control information with respect tothe fixed subframe or the RRC subframe. That is, the UL/DL structure orthe format structure for the fixed subframe or the RRC subframe ischanged to the UL/DL structure or the format structure acquired throughthe downlink control information. In this case, according to theintention of the base station, the terminal can operate through thechange of the UL/DL structure of the corresponding subframe.

Third, the terminal performs an operation with respect to thecorresponding subframe by updating (i.e., applying) the previouslyacquired information through the newly received downlink controlinformation with respect to the fixed subframe or the RRC subframe onlyat the corresponding moment. That is, the UL/DL structure or the formatstructure for the fixed subframe or the RRC subframe is changed to theUL/DL structure or the format structure acquired through reception ofthe downlink control information, and thereafter, the UL/DL structurefor the fixed subframe or the RRC subframe is changed again to thepreviously acquired information. In this case, according to theintention of the base station, the terminal can operate through thechange of the UL/DL structure of the corresponding subframe in realtime, and then can maintain again the previously configured fixedsubframe or the RRC subframe configuration.

Next, in case of operating the TDD in the 5G communication system ofFIGS. 13A and 13B, a scheme will be described, in which a subframe isdivided into a plurality of types, and it is prevented to exceed themaximum delay time during signal transmission/reception in considerationof a specific one of respective subframe types as a subframe that can bedynamically changed uplink and downlink.

FIG. 15 is a diagram illustrating a second embodiment in which a 5Gsystem for each subframe type is operated in TDD. Referring to FIG. 15,in operating the 5G communication system in one TDD carrier, allsubframes are operated as dynamic subframes, and the terminal performssynchronization signal and system information transmission and a randomaccess through another 5G stand-alone cell, and dynamically change thesubframe to match the UL/DL data in the dynamic subframes totransmit/receive data.

First, a scheme for the terminal to support the synchronization signaland system information reception and the random access will bedescribed.

Referring to FIG. 15, TDD 1500 information (carrier frequency, frequencyband (BW), and their location information) may be transmitted fromanother stand-alone 5G base station connected through carrieraggregation or dual connectivity to a 5G capable terminal, and the 5Gcapable terminal may obtain the above-described information throughsynchronization acquisition from the stand-alone 5G base station andessential system information reception.

Since all subframes are operated as dynamic subframe 1510, the dynamicsubframe 1510 may be a downlink subframe or may be an uplink subframe inaccordance with the base station scheduling. The terminal determineswhether the corresponding dynamic subframe 1510 is uplink or downlinksubframe through reception of the downlink control informationtransmitted by the base station, and performs downlink data receptionand uplink data transmission in accordance with the scheduling by thedetermined subframe and the decoded downlink control information.

FIGS. 16A and 16B are diagrams illustrating procedures of a base stationand a terminal according to an embodiment of the present disclosureoperating a 5G communication system for each subframe type in TDD.

Referring to FIG. 16A, a procedure will be described, in which a 5G basestation configures a 5G resource for each subframe type in TDD, andtransmits and receives data with a 5G terminal on the resource for the5G.

Referring to FIG. 16A, at operation 1600, the 5G base station transmitssynchronization signal and system information to the 5G terminal in afixed subframe. The synchronization signal for the 5G may be a separatesynchronization signal for eMBB, mMTC, and URLLC using differentnumerologies, or a common synchronization signal on a specific 5Gresource using one numerology. The system information may include 5Gfrequency information (e.g., carrier frequency and physical resourceblock related information), time information (e.g., radio frame index,slot related information, MBSFN subframe information for 5Gtransmission, and information for random access), antenna information,spatial information, duplex information (FDD DL and/or UL carrierinformation, TDD UL/DL configuration information, and LAA operationrelated information), a reference signal, or a synchronization signal.The system information may be transmitted as a common system signal on aspecific 5G resource using one numerology, and may be transmitted asseparate system information for eMBB, mMTC, and URLLC using differentnumerologies.

At operation 1610, the 5G base station receives a random access signalfrom the 5G terminal in the fixed subframe, and thereafter, performs arandom access process with the 5G terminal.

At operation 1620, the 5G base station transmits a signal indicating anRRC subframe to the 5G terminal. The operation 1620 may be performed incase where the 5G base station determines that the operation 1620 isnecessary. If the signal is not transmitted, the subframe type includesonly the fixed subframe and a dynamic subframe.

At operation 1630, the 5G base station transmits and receives a signalwith the 5G terminal in the RRC subframe and the dynamic subframe. Theinformation being transmitted and received and the base stationprocedure are as described above with reference to FIGS. 14 and 15.

Referring to FIG. 16B, a procedure will be described, in which a 5Gterminal receives a 5G resource configured by a 5G base station for eachsubframe type in TDD, and transmits and receives data with the 5G basestation on the resource for the 5G.

At operation 1650, the 5G terminal receives synchronization signal andsystem information from the 5G base station in a fixed subframe. Thesynchronization signal for the 5G may be a separate synchronizationsignal for eMBB, mMTC, and URLLC using different numerologies, or acommon synchronization signal on a specific 5G resource using onenumerology. The system information may include 5G frequency information(e.g., carrier frequency and physical resource block relatedinformation), time information (e.g., radio frame index, slot relatedinformation, MBSFN subframe information for 5G transmission, andinformation for random access), antenna information, spatialinformation, duplex information (FDD DL and/or UL carrier information,TDD UL/DL configuration information, and LAA operation relatedinformation), a reference signal, or a synchronization signal. Thesystem information may be received as a common system signal on aspecific 5G resource using one numerology, and may be received asseparate system information for eMBB, mMTC, and URLLC using differentnumerologies.

At operation 1660, the 5G terminal attempts a random access (i.e.,transmits a random access signal) in the fixed subframe, and thereafter,performs a random access process with the 5G base station.

At operation 1670, the 5G terminal receives a signal indicating an RRCsubframe from the 5G base station. If the 5G terminal cannot receive thesignal at operation 1670, it determines that the subframe type includesonly the fixed subframe and the dynamic subframe.

At operation 1680, the 5G terminal transmits and receives a signal withthe 5G base station in the RRC subframe and the dynamic subframe. Theinformation being transmitted and received and the terminal procedureare as described above with reference to FIGS. 14 and 15.

Next, FIG. 17 is a diagram illustrating a first embodiment for providingforward compatibility for each subframe type in TDD. In case ofproviding forward 5G phase 2 or beyond 5G technology and servicesthrough FIG. 17, a scheme for causing no forward compatibility problemin the 5G service and technical support is provided.

Referring to FIG. 17, in case of operating a 5G communication system inone TDD carrier, the subframe type is divided into a fixed subframe, anRRC subframe, and a forward compatibility subframe, and the base stationand the terminal may perform synchronization signal and systeminformation transmission and random access in the fixed subframe,perform additional system information transmission and additional randomaccess in the RRC subframe, and transmit and receive data for 5G data or5G phase 2 and beyond 5G technology and services in the forwardcompatibility subframes. Accordingly, regardless of what purpose theforward compatibility subframes are used for, the essential andadditional system operations are performed through the fixed subframe orthe RRC subframe, and thus it can be known that there is not anybackward compatibility problem in the 5G service and technical support.

First, the fixed subframe will be described. Referring to FIG. 17, TDD1700 information (carrier frequency, frequency band, and their locationinformation) may be transmitted from a 5G base station to a 5G capableterminal, and the 5G capable terminal may obtain the above-describedinformation through synchronization acquisition and essential systeminformation reception in the fixed subframe 1710. In FIG. 17, thelocation and the number of fixed subframes 1710 are merely exemplary.The location and the number of different fixed subframes, downlink fixedsubframes, and uplink fixed subframes may be determined in advancethrough the standards. The 5G capable terminal attempts to acquiresynchronization and essential system information from the downlink fixedsubframes, acquires random access related information through thereceived essential system information, and attempts the random access inthe uplink fixed subframes.

Next, the RRC subframe 1720 will be described. It is preferable todetermine the minimum number of fixed subframes 1710 in the standards.This is because, if the number of fixed subframes 1710 becomes larger,it is required to take a delay time caused by the fixed subframes intoconsideration, and the number of subframes that can be used for theforward compatibility is reduced. If uplink data transmission for URLLCis performed in the downlink fixed subframe, it is required to delayURLLC uplink data transmission until the uplink subframe appears, and inthis case, it is difficult to satisfy ultra-delay time requirements forthe URLLC. Accordingly, instead of minimizing the number and thelocations of fixed subframes 1710, it is possible to make the basestation configure the RRC subframe 1720 through higher signaltransmission in order to support service specialized system informationtransmission in accordance with the number of terminals in the cell anda random access command by the base station. The terminal acquires thelocation and the number of uplink/downlink subframes of the RRC subframe1720 through the reception of the higher signal, and performs decodingof downlink control information only in the subframe having a downlinkresource on which the decoding of the downlink control informationshould be performed in the RRC subframe 1720 to reduce decodingcomplexity.

Specifically, if there is no information on the RRC subframe 1720 fromthe base station, the terminal does not attempt decoding of the downlinkcontrol information with respect to the uplink fixed subframe 1710, butattempts to decode the downlink control information with respect to thedownlink fixed subframe 1720. The terminal determines the remainingsubframes excluding the fixed subframes 1710 as forward compatibilitysubframes 1730 in all, and attempts to decode the downlink controlinformation for each subframe. If the terminal does not receive anydownlink control information (or if the terminal receives informationindicating that the previous or post subframe or slot is for the forwardcompatibility) in the forward compatibility subframe, the terminal doesnot perform any operation in the forward compatibility subframe, and isshifted to an idle state to lower power consumption.

If the information on the RRC subframe 1720 is transmitted from the basestation and is received in the terminal, the terminal does not attemptdecoding of the downlink control information with respect to the uplinkfixed subframe 1710, but attempts to decode the downlink controlinformation with respect to the downlink fixed subframe 1710. Next, theterminal does not attempt decoding of the downlink control informationwith respect to the uplink RRC subframe 1720, but attempts to decode thedownlink control information with respect to the downlink RRC subframe1720. The terminal determines the remaining subframes excluding thefixed subframes 1710 and the RRC subframe 1720 as forward compatibilitysubframes 1730 in all, and attempts to decode the downlink controlinformation for each subframe. If the terminal does not receive anydownlink control information (or if the terminal receives informationindicating that the previous or post subframe or slot is for the forwardcompatibility) in the forward compatibility subframe, the terminal doesnot perform any operation in the forward compatibility subframe, and isshifted to an idle state to lower power consumption. Actually, theterminal may not know the existence of the forward compatibilitysubframe, and it is also possible for the terminal to determine that theterminal does not receive any downlink control information in theforward compatibility subframe.

Next, the forward compatibility subframe 1730 will be described. Theforward compatibility subframe 1730 may be a downlink subframe or may bean uplink subframe in accordance with the base station scheduling. Theterminal determines whether the corresponding dynamic subframe 1730 isuplink or downlink through reception of the downlink control informationtransmitted by the base station, and performs downlink data receptionand uplink data transmission in accordance with the scheduling by thedetermined subframe and the decoded downlink control information. If theterminal does not receive any downlink control information (or if theterminal receives information indicating that the previous or postsubframe or slot is for the forward compatibility) in the forwardcompatibility subframe, the terminal does not perform any operation inthe forward compatibility subframe, and is shifted to an idle state tolower power consumption. Actually, the terminal may not know theexistence of the forward compatibility subframe, and it is also possiblefor the terminal to determine that the terminal does not receive anydownlink control information in the forward compatibility subframe.

FIG. 18 is a diagram illustrating a second embodiment for providingforward compatibility for each subframe type in FDD. In case ofproviding forward 5G phase 2 or beyond 5G technology and servicesthrough FIG. 18, a scheme for causing no forward compatibility problemin the 5G service and technical support is provided.

Referring to FIG. 18, in case of operating a 5G communication system inone TDD carrier, the subframe type is divided into a fixed subframe, anRRC subframe, and a forward compatibility subframe for each downlinkcarrier and uplink carrier, and the base station and the terminal mayperform synchronization signal and system information transmission andrandom access in the fixed subframe of the downlink carrier, performadditional system information transmission and additional random accessin the RRC subframe, and transmit and receive data for 5G datatransmission/reception or 5G phase 2 and beyond 5G technology andservices in the forward compatibility subframes. Further, the terminalmay perform contention-based (hereinafter, mixedly used withcompetition-based) random access using the fixed subcarrier of theuplink carrier, perform additional random access triggered by the basestation (i.e., non-contention based random access can be performed usingthe RRC subframe that can be configured to the terminal, and it does notexclude contention-based random access using the RRC subframe) using theRRC subframe, and transmit and receive data for 5G datatransmission/reception or 5G phase 2 and beyond 5G technology andservices using the forward compatibility subframe. Accordingly,regardless of what purpose the forward compatibility subframes are usedfor, the essential and additional system operations are performedthrough the fixed subframe or the RRC subframe, and thus it can be knownthat there is not any backward compatibility problem in the 5G serviceand technical support.

First, the fixed subframe 1810 of the downlink carrier and the fixedsubframe 1840 of the uplink carrier will be described. Referring to FIG.18, FDD 1800 information (downlink and uplink carrier frequency,frequency band (BW), and their location information) may be transmittedfrom a 5G base station to a 5G capable terminal, and the 5G capableterminal may obtain the above-described information throughsynchronization acquisition and essential system information receptionin the fixed subframe 1810 of the downlink carrier. The location and thenumber of fixed subframes 1810 of the downlink carrier are merelyexemplary. The location and the number of different fixed subframes maybe determined in advance through the standards. The 5G capable terminalattempts to acquire synchronization and essential system informationfrom the fixed subframes, and acquires random access related informationthrough the received essential system information. The terminal attemptsthe random access in the fixed subframes 1840 of the uplink carrier. Thelocation and the number of fixed subframes 1840 of the uplink carrierare merely exemplary. The location and the number of different fixedsubframes may be determined in advance through the standards.

Next, the RRC subframe 1820 of the downlink carrier and the RRC subframe1850 of the uplink carrier will be described. It is preferable todetermine the minimum number of fixed subframes 1810 and 1840 in thestandards. This is because, if the number of fixed subframes 1810 and1840 becomes larger, it is required to take a delay time caused by thefixed subframes into consideration, and the number of subframes that canbe used for the forward compatibility is reduced. Accordingly, insteadof minimizing the number and the locations of fixed subframes 1810 and1840, it is possible to make the base station configure the RRCsubframes 1820 and 1850 through higher signal transmission in order tosupport service specialized system information transmission inaccordance with the number of terminals in the cell and a random accesscommand by the base station. The terminal acquires the location and thenumber of RRC subframes 1820 and 1850 of the downlink carrier and theuplink carrier through reception of the higher signal.

If there is no information on the RRC subframes 1820 and 1850 from thebase station, the terminal determines the remaining subframes excludingthe fixed subframes 1810 and 1840 as forward compatibility subframes1830 and 1860 in all, and attempts to decode all the downlink controlinformation for each subframe 1830. If the terminal does not receive anydownlink control information (or if the terminal receives informationindicating that the previous or post subframe or slot is for the forwardcompatibility) in the forward compatibility subframe, the terminal doesnot perform any operation in the forward compatibility subframe, and isshifted to an idle state to lower power consumption.

If the information on the RRC subframes 1820 and 1840 is transmittedfrom the base station and is received in the terminal, the terminaldetermines the remaining subframes excluding the fixed subframes 1810and 1840 and the RRC subframes 1820 and 1840 as forward compatibilitysubframes 1830 and 1860 in all, and attempts to decode the downlinkcontrol information for each subframe 1830. If the terminal does notreceive any downlink control information (or if the terminal receivesinformation indicating that the previous or post subframe or slot is forthe forward compatibility) in the forward compatibility subframe, theterminal does not perform any operation in the forward compatibilitysubframe, and is shifted to an idle state to lower power consumption.Actually, the terminal may not know the existence of the forwardcompatibility subframe, and it is also possible for the terminal todetermine that the terminal does not receive any downlink controlinformation in the forward compatibility subframe.

Next, the forward compatibility subframes 1830 and 1860 will bedescribed. If the terminal does not receive any downlink controlinformation (or if the terminal receives information indicating that theprevious or post subframe or slot is for the forward compatibility) inaccordance with the base station scheduling in the forward compatibilitysubframe 1830, the terminal does not perform any operation in theforward compatibility subframes 1830 and 1860, and is shifted to an idlestate to lower power consumption. Actually, the terminal may not knowthe existence of the forward compatibility subframe, and it is alsopossible for the terminal to determine that the terminal does notreceive any downlink control information in the forward compatibilitysubframe.

Next, FIGS. 19A and 19B are diagrams illustrating procedures of a basestation and a terminal according to an embodiment of the presentdisclosure for providing forward compatibility for each subframe type.Referring to FIGS. 19A and 19B, a method, in which a 5G base stationconfigures resources for a 5G resource and forward compatibility foreach subframe type, and a procedure, in which a 5G terminal transmitsand receives data on the resource for the 5G, will be described.

Referring to FIG. 19A, at operation 1900, the 5G base station transmitssynchronization signal and system information to the 5G terminal in afixed subframe. The synchronization signal for the 5G may be a separatesynchronization signal for eMBB, mMTC, and URLLC using differentnumerologies, or a common synchronization signal on a specific 5Gresource using one numerology. The system information may include 5Gfrequency information (e.g., carrier frequency and physical resourceblock related information), time information (e.g., radio frame index,slot related information, MBSFN subframe information for 5Gtransmission, and information for random access), antenna information,spatial information, duplex information (FDD DL and/or UL carrierinformation, TDD UL/DL configuration information, and LAA operationrelated information), a reference signal, or a synchronization signal.The system information may be transmitted as a common system signal on aspecific 5G resource using one numerology, and may be transmitted asseparate system information for eMBB, mMTC, and URLLC using differentnumerologies.

At operation 1910, the 5G base station receives a random access signalfrom the 5G terminal in the fixed subframe, and thereafter, performs arandom access process with the 5G terminal.

At operation 1920, the 5G base station transmits a signal indicating anRRC subframe to the 5G terminal. The operation 1920 may be performed incase where the 5G base station determines that the operation 1620 isnecessary. If the signal is not transmitted, the subframe type includesonly the fixed subframe and a dynamic subframe.

At operation 1930, the 5G base station transmits and receives a signalwith the 5G terminal in the RRC subframe and the forward compatibilitysubframe. The information being transmitted and received and the basestation procedure are as described above with reference to FIGS. 17 and18.

Referring to FIG. 19B, a procedure will be described, in which a 5Gterminal receives a 5G resource configured by a 5G base station for eachsubframe type and a resource for forward compatibility, and transmitsand receives data with the 5G base station on the resource for the 5G.

At operation 1950, the 5G terminal receives synchronization signal andsystem information from the 5G base station in a fixed subframe. Thesynchronization signal for the 5G may be a separate synchronizationsignal for eMBB, mMTC, and URLLC using different numerologies, or acommon synchronization signal on a specific 5G resource using onenumerology. The system information may include 5G frequency information(e.g., carrier frequency and physical resource block relatedinformation), time information (e.g., radio frame index, slot relatedinformation, MBSFN subframe information for 5G transmission, andinformation for random access), antenna information, spatialinformation, duplex information (FDD DL and UL carrier information, TDDUL/DL configuration information, and LAA operation related information),a reference signal, or a synchronization signal. The system informationmay be received as a common system signal on a specific 5G resourceusing one numerology, and may be received as separate system informationfor eMBB, mMTC, and URLLC using different numerologies.

At operation 1960, the 5G terminal attempts a random access (i.e.,transmits a random access signal) in the fixed subframe, and thereafter,performs a random access process with the 5G base station.

At operation 1970, the 5G terminal receives a signal indicating an RRCsubframe from the 5G base station. If the 5G terminal cannot receive thesignal at operation 1970, it determines that the subframe type includesonly the fixed subframe and the forward compatibility subframe.

At operation 1980, the 5G terminal transmits and receives the signalwith the 5G base station in the RRC subframe and the forwardcompatibility subframe. The information being transmitted and receivedand the terminal procedure are as described above with reference toFIGS. 17 and 18.

Next, FIG. 20 is a diagram illustrating the configuration of a basestation device according to the present disclosure.

Referring to FIG. 20, the base station device is composed of acontroller 2000, a scheduler 2010, a 5G resource allocation informationtransmission device 2020, and a 5G data transmission/reception device2030, and this may be understood as a configuration of the controller2000 including the scheduler 2010, and a transceiver including the 5Gresource allocation information transmission device 2020, and the 5Gdata transmission/reception device 2030. In accordance with a basestation procedure according to FIGS. 16A and 19A, a TDD operation schemefor each subframe type according to FIGS. 14, 15, 17, and 18 accordingto the present disclosure, and a forward compatibility subframeoperation scheme for each subframe type, the controller 2000 controls 5Gresource allocation, transmits resource allocation information to theterminal through the 5G resource allocation information transmissiondevice 2020, and transmits and receives 5G data with the 5G terminalthrough the 5G data transmission/reception device 2030 throughscheduling of the 5G data on the 5G resource by means of the scheduler2010.

Next, FIG. 21 is a diagram illustrating the configuration of a terminaldevice according to the present disclosure.

Referring to FIG. 21, the terminal device is composed of a controller2100, a 5G resource allocation information reception device 2110, and a5G data transmission/reception device 2120, and this may be understoodas a configuration of the controller 2100, and a transceiver includingthe 5G resource allocation information reception device 2110 and the 5Gdata transmission/reception device 2120. In accordance with a terminalprocedure according to FIGS. 16B and 19B, a TDD operation scheme foreach subframe type according to FIGS. 14, 15, 17, and 18 according tothe present disclosure, and a forward compatibility subframe operationscheme for each subframe type, the terminal device receives 5G resourceallocation information from the base station through the 5G resourceallocation information reception device 2110, and the controller 2100transmits and receives data with the 5G base station through control ofthe 5G data transmission/reception device 2120 with respect to thescheduled 5G data on the allocated 5G resource.

On the other hand, embodiments of the present disclosure have beenpresented to assist those of ordinary skill in the art to gain acomprehensive understanding of the present disclosure, and do not limitthe scope of the present disclosure. It will be apparent to those ofordinary skill in the art to which the present disclosure pertains thatvarious modifications are possible based on the technical concept of thepresent disclosure in addition to the embodiments disclosed herein.Further, the respective embodiments may be combined with each other tobe operated. For example, portions of the embodiments of the presentdisclosure may be combined with each other to be operated by the basestation and the terminal.

1. A method by of a base station in a wireless communication system, themethod comprising: identifying a subcarrier spacing included in asubcarrier spacing set which is available to be supported by the basestation, the subcarrier spacing set including a first subcarrier spacingand a second subcarrier spacing; and transmitting a synchronizationsignal using the identified subcarrier spacing. 2-4. (canceled)
 5. Amethod of a terminal in a wireless communication system, the methodcomprising: identifying a subcarrier spacing set which is available tobe supported by a base station, the subcarrier spacing set including afirst subcarrier spacing and a second subcarrier spacing; identifyingthat a synchronization signal is detected using the first subcarrierspacing; when the synchronization signal is detected based on the firstsubcarrier spacing, determining that the first subcarrier spacing isused by the base station; when the synchronization signal is notdetected based on the first subcarrier spacing, identifying that thesynchronization signal is detected using the second subcarrier spacing;when the synchronization signal is detected based on the secondsubcarrier spacing, determining that the second subcarrier spacing isused by the base station; and acquiring synchronization based on thedetected synchronization signal and the determined subcarrier spacing.6. The method of claim 5, wherein the subcarrier spacing set includesone of 15 kHz and 30 kHz or 120 kHz and 240 kHz.
 7. The method of claim5, further comprising: identifying a reference timing and a frequencyoffset based on the determined subcarrier spacing which is used by thebase station and the detected synchronization signal.
 8. The method ofclaim 5, wherein the subcarrier spacing set is predetermined.
 9. A basestation in a wireless communication system, the base station comprising:a transceiver; and a controller coupled with the transceiver andconfigured to: identify a subcarrier spacing included in a subcarrierspacing set which is available to be supported by the base station, thesubcarrier spacing set including a first subcarrier spacing and a secondsubcarrier spacing, transmit a synchronization signal using theidentified subcarrier spacing. 10-12. (canceled)
 13. A terminal in awireless communication system, the terminal comprising: a transceiver;and a controller coupled with the transceiver and configured to:identify a subcarrier spacing set which is available to be supported bya base station, the subcarrier spacing set including a first subcarrierspacing and a second subcarrier spacing, identify that a synchronizationsignal is detected using the first subcarrier spacing, determine thatthe first subcarrier spacing is used by the base station if thesynchronization signal is detected based on the first subcarrierspacing, and identify that the synchronization signal is detected usingthe second subcarrier spacing if the synchronization signal is notdetected based on the first subcarrier spacing, when the synchronizationsignal is detected based on the second subcarrier spacing, determinethat the second subcarrier spacing is used by the base station, andacquire synchronization based on the detected synchronization signal andthe determined subcarrier spacing.
 14. The terminal of claim 13, whereinthe subcarrier spacing set includes one of 15 kHz and 30 kHz or 120 kHzand 240 kHz.
 15. The terminal of claim 13, wherein the controller isfurther configured to identify a reference timing and a frequency offsetbased on the determined subcarrier spacing which is used by the basestation and the detected synchronization signal.
 16. The method of claim5, further comprising: changing a terminal hardware configuration toattempt to detect the synchronization signal using the determinedsubcarrier spacing.
 17. The method of claim 1, wherein the identifyingthat the synchronization signal is detected using the first subcarrierspacing further comprises: selecting the second subcarrier spacing whenthe synchronization signal is not detected based on the first subcarrierspacing during a predetermined time interval.
 18. The terminal of claim13, wherein the subcarrier spacing set is predetermined.
 19. Theterminal of claim 13, the controller is further configured to change aterminal hardware configuration to attempt to detect the synchronizationsignal using the determined subcarrier spacing.
 20. The terminal ofclaim 13, the controller is further configured to select the secondsubcarrier spacing if the synchronization signal is not detected basedon the first subcarrier spacing during a predetermined time interval.